Decor Tips - oil paintings - Huh?

Cliff Wilson

SGF, Supreme Grumble Framer
Industry Vendor
May 14, 2002
Worcester, MA
In Decor May '05 issue there is an article entitled "125 Tips for 125 Years,"

Some were quite good, some were kind of "duhh?" (way too obvious to print), and some ... well, let's just say I wasn't sure I agreed completely.

But, one I thought was just plain wrong. Under "ART" the last bullet on page 83 reads:
"Generally speaking, original oil paintings should not be placed under glazing of any kind. Oils need plenty of ventilation, and unlike paper artwork, oils may be dusted or gently cleaned. Also, be sure not to completely seal the back of an oil, as this is a leading cause of mildewed canvas."
Hugh? anybody? Isn't this the OPPOSITE of what I've been reading EVERYWHERE?
I would have to agree with them on this one Cliff. The only reason for glazing would be if there were a vandalism concern with the painting hung in a public place. The back should have a dust cover to keep out dirt and critters but should not be air-tight.
Gotta go with it Cliff, dust and critter exclusion with breathability is the #1 reason for Cambric or Tyvek.

As for glazing, the voting is still out on "fresh" oils, newer than 50 years, but Europe is way ahead of us on this as the major museums are placing "shatter-proof" Zuel glazing on as many paintings as they can.

Unlike America and it litiganous enviornment, you can take pictures in most of the major museums. So the glazing is Anti-reflective and UV protection as well. It has allowed for a higher lumin rating in the galleries as well.

But those oils are OLD and DRY. :D
Doug, I've read a few reasons, including, but not limited to, added UV filtering for some fade protection, physical damage protection (even in a house things happen), and polution and air contaminant protection. And, yes it can be cleaned, but not everyone has the time for a good and proper spit clean.

Baer, - Newer than fifty years - first time I heard that, but ok. But, it seems to me the same reasons for glazing "older" paintings applies to newer ones. And, (to paraphrase Hugh) the paintings don't have lungs.

As I recall reading ... put a board or strong backing on oils to protect against damage from behind ... cover with a dust cover to protect against dust and bugs. When I saw the "be sure not to completely seal" wording, I read it as don't "put a dust cover on." Maybe I over read that. Are you assuming the word "seal" means near airtight? I took the wording to say "don't protect the front or the back."
The best, most complete, most up-to-date recommendations for canvas are from CCI (Canadian Conservation institute).

You can buy their "CCI Notes" for art on canvas through their web site, as I recall.

I would not hesitate to glaze an oil painting that is a few years old, but I would allow plenty of insulating air gap in any case. I always use a solid-board dustcover on canvases, but can't think of a good reason to attempt any kind of air-tight seal.

Baer, is the 50-year-old recommendation your own idea, or did it come from some conservation authority?
Oil paint "dries" by oxidizing and some circulation may be helpful, initially. Glazing
an oil may slow that process, which should help
reduce cracking of the oil paint; not a bad thing.
Damp rooms, not backing materials, lead to the
growth of mold and mildew on the backs of paintings. Examples of canvases from the 19th Century in England that had wooden backing boards
show how protecting the back of the canvas from damp walls and poking in the back keep the canvas
in good shape. A sheet of Coroplast or Cor-X
screwed to the back of the stretcher bars is quite
useful in protecting the canvas, whether it is in
or out of its frame.

I have seen first hand what happens when you glaze an oil painting. A local/national bank has a museum in its loby. On the walls are various works of art and informational pieces. There are a series of portraits on the wall of the founders of the company. These paintings are roughly 100years old give or take. 10-15 years ago these oil painting were glazed. On the inside of the glazing now it looks like an oil slick. kind of like the look of museum glass with smears or fingerprints on it. I'm in the process of convincing the currator that they need to take the glazing off the paintings.

As far as a dust covering on the back of the canvases. You can and should provide a backing for the painting to provide protection from damage. It should have the ability to breath though. I usualy cut a backing to size but cut the corners off exposing to just inside the inner dimension of the stretcher bars.

If you must protect the front with some sort of glazing, I would suggest an encasement for it that has side ventalation for the artwork and can be easily removed and cleaned. I had one client that went to the extent of having a local museum create an environmentaly controled plexi case for an important piece that was going to be in an area detrimental to the artwork.

I would have to agree 100% with the tip. Although it is generalized and as with all generalizations it can have variables.
Jim, when I was in Amsterdam, at the Rijks museum, I was curious about the glazing on oils. So I asked.

I was informed that if the painting had no major restoration in the last "Half Century" (I took that to mean 50 years) then they felt that it was prudent to place the glazing.

Remember, in Europe, you can (but shouldn't) touch the frames and paintings. They don't rope off access like we do here in America.

When we got down to the Louvre, they also concurred the policy of "Half Century" . . but then they have all that old wine . . . so I figured maybe in France it means 60 years. But what do I know, I'm just the nose picker standing in the middle of the gallery enjoying the FRAMES. :D
I like your coment about looking at the frames. My wife and I went to the Met on a trip to New York. I took many photographs while we were there (without flash of course). When we got home and we were looking at the pictures I had taken my wife's question was "Why do we have all these pictures of frames? Where's the art at?"
Like most things in life, it depends.

Oil, like any other medium, can have a number of of formulations. Some are more successful and/or stable than others. Some oils (usually artist's experiments) never dry.

Glazing protects from mechanical damage, and some chemical damage (air pollution). Unvarnished paintings are very vulnerable to soiling.

Volatiles released from curing/oxidizing paints and printing inks can indeed sometimes fog the inside of glass. Putting a sheet of Artcare behind the art might absorb these, and prevent the fogging. Or, watch to see if there is a problem and then clean or change the glass if there is.

The trend now is to keep the backboard solid - no cutouts for breathing as it was found to be unnecessary, and could actually be harmful. The cut-outs were found to act as chimneys, drawing dirty air in. Also they seemed to amplify vibration of the canvas during transit, causing the canvas to "drum".

I agree totally, Rebecca. Another thing cut outs are good for is an easy entrance to a home for insects....which eventually die and fall down between the canvas and stretcher and make very harmful bumps in the canvas.
When I had my retail shop, I had glass shelving which had to be washed every week because it would get cloudy looking, no matter what I cleaned it with. I've taken many pictures apart and usually they will have clouding inside. Does anyone know definitively what causes this clouding? Has there been tests done on it? I understand that everything out gasses, but does the outgassing cause harm? Is the clouding harmful to the art? Does paper cloud like glass or is it just a glass thing? Doesn't most or all old glass have clouding?

Just wondering....
Nona, the clouding can be any number of things.

Tim Padfield, a conservation scientist, did some analaysis on the crystals that precipitated on the inside of the glass on a framed sampler, and found detergents. Another study found dyes. I'm sure in frames with printing inks and oil paint it's organic acids and such that are emitted during the curing process.

The fog can be the condensation products of the vaporous acids etc. as they hit the cooler glass, or it can be leached detergents or dyes or whatever from something that is touching the glass and went through a wet/dry cycle with changing temperature and humidity.

I'm sure it s not "good" for the art, and could be a reason to use Artcare, and spacers, and keeping things in a reasonably stable environment.

Paper doesn' cloud like glass, but it can get a build up of deposits on it too. But the glass is more likely to get it because it is cooler than paper, and so vapors will condense on it first.

Originally posted by briank:
I have seen first hand what happens when you glaze an oil painting...10-15 years ago these oil painting were glazed. On the inside of the glazing now it looks like an oil slick... I'm in the process of convincing the currator that they need to take the glazing off the paintings...
Are you saying the glazing is damaging the paintings? Please explain further.

A film coating inside frame glazings is a common occurance on all kinds of framed art & objects. The usual procedure is to clean and refit; we don't normally suggest eliminating the glazing.

The film-coating issue certainly is not unique to glazed oil paintings, and it is not necessarily a problem for the painting.

Glazing has protective value that far outweighs the inconvenience of cleaning it occasionally. Unless there's reason to believe the glazing is detrimental in some way, why not clean and refit it?
The commonest thing one finds clouding glass in
salt NaCl, which has nothing to do with oil paintings. As Jim said, periodic cleaning of the
glazing should be part of the maintenance of works
in frames and it is a tiny price to pay for the
preservation value that glazing affords.

Did I miss a mention in this thread about spacers under the glazing?

In case it isn't anywhere above, it's worth saying that the air gap between the glazing and the art -- whether it's oil paint, watercolor, or other medium -- represents insulation. That is, it helps to slow the rate of change of temperature and humidity within the closed-up frame package, which may be a key benefit for art on canvas.

I guess it's obvious that glazing an oil painting without a spacer would lead to serious problems, as it would (at least) affect texture and would probably stick.
I guess what I'm asking, and maybe it needs a new thread, is that if I put a fabric that does not touch the art but might have acids, a fillet placed an inch away from the opening of the mat directly on the art with a metal barrier tape under it, does the outgassing hurt the art anymore than it would be harmed hanging in most home environments? I've heard people use the clouded glass as a reason to keep everything inside the housing as pure as possible. Purity would be the ideal, but as a retail custom framer, seldom can the ideal be met. If I have the art in a protective package, 8-ply mat, 4-ply preservation grade backboard, especially with artcare, hinged correctly and the art is an inch away from a wooden frame, can my conscience be clear?

It seems the clouded glass is saying that pieces, either canvas or paper, do need to be inspected and cleaned every five years at least.
Maybe I'm missing something regarding glazing oil paintings. I have never seen any advocation for the glazing of canvases from any repudable source. Yes you CAN glaze it and clean on occasion. But in my years working with fine art consultants, fne art conservators, and currators of both public and private fine art collections I have never once seen a painting glazed or suggested to be glazed by any of them. I am not a conservator and don't completely understand the science of why you should or shouldn't glaze a painting but I will rely on my experiences with those that do.
The most valuable paintings in many museums are
under anti-reflective, safety glazing. This affords protection from unintentional damage from
visitors, who may use pamphlets to point out parts
of the design to one another, or who may in speaking too close to the painting, accidentally
expectorate on the paint. Paintings on wooden
panels are routinely sealed in microclimate enclosures with safety glass, when they go out
on loan. The collection of the Norton Simon Museum
is glazed to protect the paintings as are most
works by Leonardo and Vermeer in other musuems.

Nona, I think your conscience can be clear. If the piece is very special and you want to be extra extra careful, wash the fabric to remove sizing.

Brian K, although it is not traditional to glaze oil or panel paintings, nowadays it is not that unusual either. It depends on the fragility of the piece, how irreplacable it is, and how exposed its environment is. As Hugh says, lots of museums glaze paintings, though some, like the Courtauld in London have a general "non-glaze" policy, for aesthetic reasons. But policies are subject to change according to circumstances.

Hmm... I assume there is a an article or some kind of scientific paper that has been written on this subjuct. Does anyone have one or know where to find one. I would hate to base my practices on such vital things on what some people sometimes do without truely understand why it is ok or not ok to do it.

As you say Rebecca it is traditional to not glaze art and I tend to do things the traditional way until science tells me I should not. The wine industry is trying to help the aging of their wines by converting to screw caps because of cork's problems with mold spoilage. But tradition dictates that you use cork. Sometimes It is hard to buck the trend of tradition even when it is for the good of the product. I would love to see WHY I should glaze over not glaze art.
Brian I am going to make an exception an open my mouth where my opinion isn't needed. You said >>>>
I have never seen any advocation for the glazing of canvases from any repudable source.<<<

Are you aware of to whom you are speaking to and what they do for a living?

Also it if helps the discussion any I had for a long time ,a glass I had removed from a paper born etching that had a PERFECT MIRROR IMAGE of a ghostly grayish powder on the glass of the art it covered.This was to the extent that you could read the signature.So if this ghostly clouding does occur on paper born art as well and the etching is properly spaced as well as the oil painting then the clouding just may be a necessary evil for all art and should be perodically cleaned off as Jim,Hugh and Rebecca seem to be suggesting.Certainly we aren't going to suggest that we don't glaze paper art due to the clouding of it's glazing. Are we?

I think that this discussion, has digressed into one of those "framing nerd" realms.

The original question was about a statement in DECOR, which addresses as Nona points out: Retail Framers. Which is about 98% of us.

I'm sorry that I brought up the newish trend of Museums. Mia colpa, mia colpa.

Most of us will never see anything that approaches the level of art that Hugh deals with. Not even Jim, I would think.

So discussion of the minutia of what is the chemical breakdown as borne out with an atomic spectromitor and whether it is doing the kind of damage that will distroy the art in our customers life times....

I just gotta fall back on the question.... would this customer spend the few hundred dollars for a concervator to restore or even clean this painting. Only about 2% would say maybe yes.

And yes, I DO know that what I frame today is more than likely the next generations landfill. It also doesn't make it wrong.
For Nona:

Don't worry too much about glazing though - I found another article that described finding these things on the art itself in glazed and unglazed circumstances.

September 1998 Volume 21 Number 1


Evaporation of Fatty Acids and the Formation of Ghost Images by Framed Oil Paintings
by Michael R. Shilling, David M. Carson, and Herant P. Khanjian


On occasion, oil paintings are framed with a protective glass layer to prevent damage from vandalism and accidents. Over time hazy films, termed "ghost images", may appear on the inside surface of the protective glass which, ultimately, impair proper viewing of the painting. To enhance visibility, these so-called "ghost images" are periodically removed by museum preparators using glass cleaners.

Studies by Williams at the Canadian Conservation Institute, using infrared spectroscopy, determined that ghost images consist almost entirely of palmitic acid (Williams 1989). To explain his findings, Williams speculated that volatile ketones are released by the paint, some of which undergo oxidation on the glass surface to form palmitic acid.

Somewhat later, Michalski postulated another explanation for Williams's findings, that free fatty acids simply may evaporate from the painting and condense on the glass. He reasoned that enrichment of the image in palmitic acid occurs because the boiling point of palmitic acid is much lower than that of stearic acid (Michalski 1990). However, these ideas were never subjected to experimental verification.

Thus, a study was undertaken at the Getty Conservation Institute to further elucidate the composition of ghost images, and to determine whether evaporation may, indeed, play a role in the loss of fatty acids from oil paints. Thermogravimetry (TG) was used to determine the evaporation rates of palmitic, stearic, and azelaic acids in an inert gas atmosphere. Additionally, gas chromatography-mass spectrometry (GC-MS) was used to analyze ghost images that evolved from numerous test paints, to identify the materials that were present in the images and to determine which paints were most likely to produce ghost images.

Thermogravimetric analyses were conducted on samples of free fatty acid. The samples were heated from 25° C to 300° C using various heating rates. Sample weight was recorded as a function of temperature for each test, and subsequently plotted as percent of original weight versus furnace temperature. A reaction that leads to weight loss (such as evaporation) will give rise to a step on the TG curve.

Each set of TG test results were processed using a thermal analysis kinetic evaluation program to obtain routine Arrhenius equation kinetic parameters (activation energy and reaction rate). From the kinetic data, calculations were performed in order to estimate the half-time of the evaporation rate (i.e., the amount of time that would be required for one half of the fatty acid sample mass to evaporate) for a number of ambient temperatures.

Reaction rate and half-time data for the evaporation of the three fatty acids, calculated at four reference temperatures, are listed in Table 1. Based on kinetic evaluation of the TG data, the estimated half-time for the rate of evaporation at 25° C is approximately 40 years for palmitic acid, 140 years for stearic acid, and 80 years for azelaic acid.

Table 1. Reaction rate and half-time data calculated at four reference temperatures, for the evaporation of palmitic, stearic, and azelaic acids. palmitic acid stearic acid azelaic acid
T,(C) rate, 1/sec t1/2 rate, 1/sec t1/2 rate, 1/sec t1/2
25 6.1E-10 36 years 1.6E-10 136 years 2.7E-10 82 years
50 9.7E-09 2.3 years 3.0E-09 7.3 years 4.5E-09 4.9 years
80 1.6E-07 50 days 5.8E-8 137 days 7.9E-8 102 days
100 8.1E-07 9.9 days 3.2E-07 25 days 4.1E-07 20 days

In addition to TG analysis, ghost images were generated artificially for GC-MS testing purposes. Oil paint samples were placed onto single-depression microscope slides, a second slide placed onto the first with the depressions facing together, and the two slides clamped together. Duplicate samples of each paint formulation tested were placed in separate slide assemblies, with one sample kept on a sand bath set to 80° C for a six week period, and the second exposed to light in a Heraeus Suntest chamber for four weeks, followed by sand bath heating for one week. The test paints used in this study had been stored in the laboratory for up to five years prior to testing (Schilling et al. 1997).

Ghost images which developed on the upper slide well were rinsed with diethyl ether into sample vials, derivatized with Methyl-8 reagent, (from Pierce Chemical Company), and the fatty acid methyl esters were analyzed by gas chromatography-mass spectrometry (GC-MS).

Ghost images were formed by a majority of the paints, but the intensity varied with the type of exposure and the paint formulation. For the sand bath samples, no visible images were produced by cold-pressed linseed and stand linseed oil paints, and the others tended to produce images with variable intensity. On the other hand, much less intense images were formed by the Suntest exposure, but nearly all of the paints formed some visible residue.

Table 2 lists the fatty acid molar ratios for the ghost images formed by the test paints. Although the GC-MS results revealed that high levels of palmitic acid were indeed present in the images, other fatty acids were also detected, such as stearic acid, azelaic acid, and short-chain dicarboxylic fatty acids.

Table 2. Fatty acid molar ratios for ghost images generated by test paints, determined by gas chromatography-mass spectrometry. For entries with a dash, one or both of the fatty acids in the appropriate ratio could not be detected. Sandbath Suntest
Medium Pigment A/P P/S A/D A/P P/S A/D
Blown Linseed Lead White 0 11.9 - 1.3 2.3 0.5
(P/s=1.8) Vine Black 0.2 6.4 2 1.5 1.9 0.4
Yellow Ochre 0.4 4.5 1.3 0.4 2.5 0.7

Cold-Pressed Linseed Lead White 0 2.8 - 0 0.9 0
(P/s=1.7) Vine Black 2.1 - 1.7 3.1 1.8 0.9
Verdigris - - 0.2 0.9
Yellow Ochre - 2.4 5.1 1.9 1

Egg Yolk Lead White 0 5.2 - 0 4.1 1
(P/s=3.3) Yellow Ochre 0 5.6 - 0 1.8 -

Stand Linseed Lead White - 0.2 1.1 0.7
(P/s=1.8) Vine Black 0 - - 0.9 2.1 0.8
Verdigris - - - 0 1.3 -
Yellow Ochre - - - 0.3 2.3 2

Walnut Lead White 0.1 4 - 0.1 2.2 2.4
(P/s=3.3) Vine Black 0.2 - 0.9 0.4 1.9 1.6
Yellow Ochre 6.4 2.3 1.8 0.9 3.5 1.1

In general, the chromatograms for the sand bath samples were dominated by high levels of saturated fatty acids. The fatty acid compositions in the sand bath ghosts were proportional to the levels of free fatty acids present in the paint samples, but in every instance the ghosts were enriched in the more volatile, lower-boiling species. Accordingly, the P/S ratios of the sand bath ghost images were higher than that of the corresponding paints. On the contrary, paints exposed in the Suntest chamber often formed images that were enriched in dicarboxylic fatty acids, thus providing evidence for the role of light in oxidative breakdown of oil paints.

An additional test was performed to determine what effect molecular weight would have on the extent of fatty acid evaporation. A standard mixture of free monocarboxylic fatty acids (C12, C14, C16, C17, C18, and C20) and dicarboxylic fatty acids (C7, C8, C9, C10) was placed in a glass slide assembly and heated on the sand bath in order to form a ghost image. Upon examining the slide assembly after it was heated on the sand bath, a pronounced white ghost image was visible on the upper slide well, and a much smaller amount of residue remained in the lower slide well. The ghost image that developed on the upper slide well, and the residual fatty acids that remained in the lower slide well, were derivatized individually using Tri Sil reagent, (from Pierce Chemical Company), and analyzed by GC-MS.

Figure 1 is an overlay of GC-MS chromatograms of the silyated extracts from the upper slide well (a), the lower slide well (b), and an untreated fatty acid standard (c). It is clear each of the fatty acids present in the standard, both monocarboxylic or dicarboxylic in nature, were detected in the ghost image.

Furthermore, the ghost image is significantly enriched in the lower molecular weight fatty acids, whereas the residue in the lower slide well is depleted in the lower molecular weight fatty acids. Area ratios of the peaks in the ghost image versus the residue in the lower slide reveal a 5:1 enrichment for both azelaic acid and stearic acid in the ghost image, and a 16:1 enrichment for palmitic acid in the ghost image.

In analytical studies of aged oil paints conducted a number of years ago at the Getty Conservation Institute, it was discovered that the saturated fatty acid content of drying oil paints may be reduced by exposure to heat and light (Schilling et al. 1997). The largest overall reductions in saturated fatty acid content were observed for heat-aged paints made from yellow ochre mixed with walnut or poppy oil, but many of the other slow-drying paint formulations exhibited moderate reductions.

At the time, these findings were somewhat surprising because saturated fatty acids were believed to be relatively stable marker compounds in drying oil media. In fact, the relative amounts of palmitic and stearic acids are the basis for a method of identification of drying oil media that has been in practice for more than thirty years (Mills 1966).

However, in light of the present study, it is clear that evaporation does play a role in the reduction of saturated fatty acids from the test paints. The TG results demonstrate that saturated and dicarboxylic fatty acids evaporate readily, even when extremely low heating rates were employed. Interestingly, on close examination of glass sample vials that contain oil paint samples we have also observed hazy films on the inner wall of the vials, primarily near the samples.

The TG data are in broad agreement with the observed high levels of palmitic acid in ghost images, although strict comparison between half-time estimates and the composition of ghost images from the test paints is not possible due to limitations in the design of the experimental apparatus.

Williams observed that ghost images were most intense over dark colors and less intense over light colors, which gave rise, more or less, to a negative ghost image of the painted subject. Based on the results from the present study, we may offer an explanation for this phenomenon. In general, slow-drying paint formulations tend to produce intense ghost images enriched in saturated fatty acids; this is consistent with the mechanism of partial hydrolytic decomposition of the triglyceride oil matrix (Boon JJ, Peulve SL, Van der Brink OE, Duursma MC and Rain-ford D, 1996). Paints that were slow to dry include those pigmented with ochre or vine black, or made from walnut or poppy oil media. In addition, ghost image formation was greatly reduced over paints made with lead white and verdigris, presumably due to formation of pigment soaps (Koller and Burmester 1990). Thus, variation in ghost image intensity may be due strictly to the quantity of free fatty acids in paints, which in turn is affected by the specific combination of pigment and medium.

In published studies of crystalline bloom on contemporary art pieces (Koller and Burmester 1990), it has been observed that oil-rich paints made with pigments that do not promote cross-linking (such as alizarin, titanium dioxide, and ochres) are particularly susceptible to the formation of whitish surface deposits of fatty acids. Presumably, the fatty acids were released either from the oil matrix through hydrolysis of the glyceride ester backbone or else from decomposition of pigment extenders (such as stearates), and once liberated were able to migrate through the paint and deposit on the surface. Therefore, these works should be extremely likely to lose fatty acids through evaporation and, if framed behind glass, form ghost images.

Using thermogravimetry and gas chromatography-mass spectrometry, free fatty acids were shown to evaporate readily to form ghost images over oil paints. By expressing evaporation rates in units of half-times, palmitic acid was found to evaporate approximately four times as rapidly as either stearic acid or azelaic acid at room temperature.

Ghost images were found to consist of mixtures of free fatty acids, with higher levels of the more volatile species predominating in both homologous series of fatty acids. Images formed by the heating of test paint samples tended to consist largely of saturated fatty acids, whereas the composition of images formed by exposure of paint to light generally were more enriched in dicarboxylic fatty acids.

Free fatty acids are liberated by hydrolysis of oil triglycerides, migrate through the paint, and subsequently evaporate to form ghost images. In general, slow-drying paints yielded more intense ghost images than did fast-drying paints, presumably because of variation in the degree of hydrolysis of oil triglycerides.

Boon JJ, Peulve SL, Van der Brink OE, Duursma MC and Rainford D, 1996. Molecular aspects of mobile and stationary phases in ageing tempera and oil paint films. Early Italian Paintings Techniques and Analysis, Limburg Conservation Institute, Maastricht. 35-56.

Koller J and Burmester A, 1990. Blanching of unvarnished modern paintings: a case study on a painting by Serge Poliakoff. In: Mills JS and Smith P, eds. Cleaning, Retouching and Coatings: Technology and Practice for Easel Paintings and Polychrome Sculpture: Preprints of the Contributions to the Brussels Congress. London: 138-143.

Michalski S, 1990. A physical model for the cleaning of oil paint. In: Mills JS and Smith P, eds. Cleaning, Retouching and Coatings: Technology and Practice for Easel Paintings and Polychrome Sculpture: Preprints of the Contributions to the Brussels Congress. London: 85-92.

Mills JS, 1966. The gas chromatographic examination of paint media. Part I. Fatty acid composition and identification of dried oil films. Studies in Conservation 11: 92-107.

Schilling MR, Khanjian HP, Carson DM, 1997. Fatty acid and glycerol content of lipids; effects of ageing and solvent extraction on the composition of oil paints. Techne 5: 71-78.

Schilling MR, Carson DM, Khanjian HP, 1998. The composition of solvent extracts from oil paints. Art et Chimie - La Couleur conference, the Louvre.

Wendlandt WW, 1974. Thermal methods of analysis. Second edition. In: Elving PJ and Kolthoff IM, eds. Chemical analysis, volume 19. New York:Wiley and Sons:45-61.

Widmann G, 1982. Kinetic measurements on polymers-applications and limits. Journal of Thermal Analysis 25:45-55.

Williams SR, 1989. Blooms, blushes, transferred images and mouldy surfaces: what are these distracting accretions on art works? Proc. of the fourteenth annual IIC-CG Conference, IIC-Canadian Group, Ottawa. 65-84.


[ 05-17-2005, 03:53 PM: Message edited by: Rebecca ]
Ok, what I have been saying to my customers, and why I posted in the first place is:

"Glazing and a solid backing is recommended for the long term preservation of paintings including oils. Not using glazing is traditional and the painting will probably still last for your lifetime. Unless an artist INSISTS, I will continue to put a solid board and dust cover on the back of all canvas paintings. Paintings don't need to "breath.""

Hugh, you recommended coroplast or the equivalent. I have been using 4-ply rag, coroplast, or Artcare foam depending on how much space is in the rabbet. then using points to hold the package in, with a dust cover over it.

I think the questions and observations are interesting. There are no right or wrong answers, it all depends on the individual piece, the environmental circumstances, and the owner's needs.

It's not wrong to glaze oils, and it's not necessarily right either. It just depends. We get into trouble and needless strife when we try to make hard and fast rules. Guidelines are great, but it all boils down to trying to predict what works best in a world of variable dangers. The best we can do is to make an educated decision based on our own particular circumstances, keep an eye on things and change our minds if need be.

Wow. Thats great Rebecca, thanks.

That might explain why the lower fatty acid content of the oils of antiquities have less molecular decompesition and are relatively the same density centurys later, as appossed to the colapsing structures of Dada, Renoir and Andy Warhole.

It also goes to show what a low fat diet can do to reduce the impression of your ghost. :D
Originally posted by briank:
Hmm... I assume there is a an article or some kind of scientific paper that has been written on this subjuct...I tend to do things the traditional way until science tells me I should not...
Refer to AIC and CCI, and check with all of the experienced authorities you can find. The more opinions you gather, the more confidently you can make your own conclusions.

It's a matter of perspective. You have a correct perception of the "art community". They are mostly concerned with the view of the art. They presume that glazing affects the view, and is therefore not desirable. They'll need a good reason to use glazing.

The "preservation/conservation community" has a different perspective. They know first hand of the harm that can come to an exposed painting, and so they seek to protect it. They'll need a good reason not to use glazing.

Here are a few observations:

1. Glazing is a protective measure. When the custodian of an oil painting is concerned about soiling; harm from environmental changes or expansion/contraction cycles; insects; light damage such as fading, discoloration/color shift, embrittlement; mechanical damage such as pokes, scratches, abrasions, cuts ; then glazing seems wise.

2. Regarding view of the image, the anti-reflective coated glass & acrylic glazings available today are nearly invisible when they are lighted properly.

3. When properly fitted, glazing can not harm the art.

It is almost certain that at some time in history, man needed a good reason to wash his hands before eating.
I agree with Rebecca. But if at all possible glazing shouldn't be used, as it compromises the integrity of the oil painting & the original intention of the artist. If the painting is damaged & its environment isn't good, then thats another matter.
Also as an artist, everything I have read ( and seen professional oil painters use),over the years, supports the idea of using a backing,but not airtight, as it needs air to circulate. The circulation is needed to prevent moisture& mold. But I think I remember reading it needs to breathe because of how oils dry, top layer first. Honestly, I'd have to research that more, (I've been painting with pastels for years,so I'm out of the loop with oils. But just wanted to give you another perspective.

This is a great thread! This is the type of information I was hoping to find here at the grumble when I joined just a few weeks ago.

A. I do realize who I am speaking to here and mean no disrespect by using the term "repudable". I to work on art that hangs in museums. Name the artist and I've framed his/her work. I am not saying this as a way to impress but to let you understand that the decisions I make regarding the handling and treatment of artwork can affect the value of multi-million dallar works of art.

B. I loved that article but I would have like to see them make some reference as to how the glazing may or may not alter the drying process of the paint.

C. Baer, that was one heck of an informed sentance.

D. It seems that the museums are using glazing as a means of protecting the art from physical damage. I wonder if these paintings were not as easily accesable to the public if they would still glaze them?

E.Sharon, I think you have a certain point about artistic intention but us picture framers change that all the time.
Welcome, Sharon.

A pastel artist, eh? That's ANOTHER can of worms. When you get an hour or six, check the archives for threads on pastels. We'll be pleased to hear your opinions on the fixative, matting, and glazing debates whenever you're ready.

But back to the topic...

Originally posted by srw19artist56:
...if at all possible glazing shouldn't be used, as it compromises the integrity of the oil painting & the original intention of the artist...everything I have read...supports the idea of using a backing,but not airtight, as it needs air to circulate. The circulation is needed to prevent moisture& mold...
Speaking technically, it is true that airtight framing would not be good for an oil painting, or most other artworks, either -- not in the real consumer world, anyway.

But the package should slow the rate of change of temperature and humidity as much as possible. That is, circulation of air is not necessary, and open air exposure to dirt & insects is not good. Rebecca mentioned the "chimney effect", which would actually draw nasties into the framing.

But nevermind that. Perhaps this is as much a philosophical discussion as a technical one. Here are some questions we might ponder, as artists and framers:

If glazing "compromises the integrity of the oil painting & the original intention of the artist" would you say the same is true for all art? How about a watercolor, or a photograph, or a pastel?

In the absence of specific framing instructions from the artist, how would we know if/when an artist intends his/her art to have glazing?

Why is the glazing/no glazing choice a matter for the artist to decide in the first place? Should it more rightly be left to the gallery owner, who is responsible for its safety on display? Or should it be left to the art buyer who ultimately pays to love it, and expects it to endure?

In case you reaffirm that the artist is to be the glazing decision maker, here's the next question: Should the artist also specify what kind of glazing (if any) to use?

At what point does the art become the province of a person other than the artist?
Originally posted by Jim Miller:
Why is the glazing/no glazing choice a matter for the artist to decide in the first place? Should it more rightly be left to the gallery owner, who is responsible for its safety on display? Or should it be left to the art buyer who ultimately pays to love it, and expects it to endure?

In case you reaffirm that the artist is to be the glazing decision maker, here's the next question: Should the artist also specify what kind of glazing (if any) to use?

At what point does the art become the province of a person other than the artist?
Well, following the logic that if you can't trim a piece of art because it changes the way it looks, whether you can or have to glaze it and if so, with what, is just one step further down that rosy path.
If glazing "compromises the integrity of the oil painting & the original intention of the artist" would you say the same is true for all art? How about a watercolor, or a photograph, or a pastel?

No, Its not the same for all art. The very nature of the oil medium & its properties, when dried & varnished becomes a protection to the art.

I can guarentee you the there isn't an oil painter on the planet, that after finishing an oil on canvas prepares to have it framed under glass. Preserving historical or damaged paintings are the exception.

As for watercolor, pastel & photography. These are mediums on paper that their integrity would be ruined without glazing. The mediums are not designed to be a protective finish on the paper.

Every artist working in pastel & watercolor (or any medium where the paper is exposed), intends to have it glazed when framing.

The nature & properties of the medium, & its condition, has to dictate glazing.
An interesting case indeed. They didn't talk about where the piece had come from to cause such extensive damage though. Any idea what is meant in this case by "humidity controled"? Is there an active system in this case maintaining the humidity or is this a more passive concept, meaning that because it is sealed completely the environment it is in is stable?

I think in the end this thread proves one thing. In framing, just like life, there are no absolutes. I can definetely se cases for both glazing and not. I think in most cases I will keep on the non-glazed side of life but will from now on keep my eyes open to glazing.
Hi Brian -

In this case the humidity control was preconditioned silica gel called ArtSorb. So passive in that it doesn't require anything mechanical. It comes in sheet form, that you can slip into the back of the frame. Then it has to be sealed up air tight - they used Marvelseal 360 for that. Hugh has written a very good article (Picture Framer's Magazine?) on sealed framing systems.

Panel paintings are really fragile, especially in our modern world of central heating and big windows. Changes in temperature/humidity can cause the panel to flex, creating cracks and causing the paint/ground to flake.

In the old days (really not that long ago at all!) restorer/conservators tried to immobilize the panel by thinning it and mounting it on a "cradle" - something like the criss/cross structure of a Japanese screen. That created problems of its own.

Some oil paintings are inherently fragile - bad adhesion between canvas/ground and paint layers - and so are better off in a controlled environment that slows changes that can cause the different layers to move or vibrate.

Alot of "treatment" now is preventive, and tries to even out environmental fluctuations by creating mini-environments - like closed and sealed framing sytems. These are easier to create and maintain than than the huge HVAC systems in large, well financed museums and art galleries. Anything that slows down environmental changes helps keep the art stable.

I agree, it's been a fun thread.

James, Artcare is the Bainbridge's brand name for a kind of matboard that has little molecular traps in it called zeolites. They've been engineered to absorb typical gaseous pollutants that are in the air, and that are emitted by deteriorating art works. A nice passive system that doesn't require complicated mechanics.

Wow, maybe that proves my point, I'm not sure. How many framers that you know could read that and understand it? I sure couldn't.

I think what I want is a standard for retail framers that is adhered to by all custom framers and I think that can be accomplished if the standard is clear enough to be understood and flexible or realistic enough for framers to still make money. I add a lot to my bottom line with fabrics, fillets and decorative mats. If an original Rembrandt came to me to be framed, I would refer it on, I would not be qualified to do it and I wonder how many framers would be.

"Things are just right once you realize they're never going to be just right." Absolutely!!

Rules, techniques, materials, everything keeps changing. Everything is not known by the experts, forget about us poor slobs who are not experts, (count me as first in line for the slob designation), but I do not want to hurt art. Preserving and protecting art is getting more and more complicated, but standards must not change day to day. It gets overwhelming, as this whole thread proves. Standards for retail framers have to be logical and a something a retail framer can live with.

Rebecca, you are something else. Anyone who doesn't read TG is nuts and we are so lucky to have people like you and Hugh to help us out.
I didn't mean that statement I made for the artcare, I meant that for the long post. You guys are too fast for me.
Brian ,First WELCOME and let me apologize for my comments that may have slighted your credentials as a Museem Framer but I didn't notice them in your profile. However Rebecca, is a Canadian Conservator ,Hugh is a conservator employed by the National Gallery of Art and Jim and Nona are both well known supporters and Members of the FACTS and PPFA committees.

I on the other hand have to rely on the information supplied by others ,which has been coming for a long time in contradiction to this theroy.

To that end I would like to suggest that you use the search feature here on TFG and go to;f=1;t=001346. This is the Thread titled Glassing Needle Art and was posted back on 2/17/ 2001 @ 8:53 pm By KIT.

When reading it please scroll down to the post by Orton Cardberry on the topic of Glazing Oils and the responses of Rebecca. Please note the date and the acceptance of the theory then and I think if you do a further search you may find more detailed explanations by Orton of how he effectively achives this processs and why. Also be advised that I have been instructed in the Recertification of the CPF that Glazing was not only acceptable but desired. Also I hope you can accept that MOST framers make rather poor artist and the converse is also true,since everyone is plying their given trade.

However as I said I have no impressive credentials nor lofty clientel but I do pay close attention to the likes of Orton,Hugh Phibbs, Rebecca, Jim Miller ,Nona Powers and many others who have long since changed their opinions about the necessity of allowing oils ,needlework and the like to breath or be open to the air.

But then as I said this is just MHO.And it and a buck might get you a cup of coffee.LOL
Originally posted by nona powers:
Standards for retail framers have to be logical and a something a retail framer can live with.
And THAT fell out of Nona's mouth. :D I love this forum.

Rebecca, Zeolite is a naturally occuring and mined mineral. There are three mines, two in the US and one in Australia.

It is NOT engineered, other than being crushed to standardized sizes. The Zeolite that is in Artcare, ZeoNat, EndStink, and about 40 other products is the crystaline structure refered to as Zeo127. It has the strongest Positive charge for attracting negative charged stinks, smells, and other off-gases.

It is also one of the more benign agents used in Kitty litter today.

It's one drawback is that at the temperature range of 140 degrees F, it's polarity reverses.

I have use 2lb bags of this stuff for years to remove cat urine smell, and cigar smells from houses. In the summer, I take the bags to the desert for a couple of days to "expell an flush the system" as it were. Trust me when I say, "you don't want to be down wind".

If you want, I can send you a sample of this off white powder... but the postal groups have issues about powders.... so maybe I'd have to bring it to you. :D
Baer we've had this discussion before! : )

There are lots of kinds of zeolites that perform in different ways. The ones in Artcare were - maybe engineered is the wrong word maybe it's not, let's just say "chosen" because they performed as described. Others have different characteristics and are used in other capacities.


[ 05-17-2005, 11:06 PM: Message edited by: Rebecca ]
I used to have the first page bookmarked but then . . . well . . as computers sometimes do....mine played unsafely.... and the page went away.

And that was a few . . ok more than a few years ago. But when I went to try and find anything on Manufactured aluminiosilicates and other cage structures, it was like they never exsisted.

Now you bring me the most important page (the WAAC) for everything I've been pounding the pulpit on about how and why....

I owe you a big hug and a kiss on the cheek. You're the greatest.

And for anyone else who seriously reads the WAAC page top to bottom.... yes, I am THAT much of a geek. :D

Nona, read it untill it make sense. About the time you get down to the duck picture, it's gotta start sinking in. Rebecca is the greatest.
Hello all,

I've been lurking here for awhile and as a painter and a framer I have to put my two cents in on this one. Oil paintings on canvas were never meant to be glazed. The artist never expected there to be a barrier between the viewer and the piece. That said, the relative value of a Vermeer may justify the compromise. There is an immediacy to a painting that you don't get with a print or a drawing simply because there is no glass between you and the art. I never glaze a painting on canvas for no other reason than aesthetics, and I always defer to the intent of the artist.

Now if you really want to open a can of worms lets talk about oil paintings on paper! I tell all my customers that bring in paintings on paper that this is a dilemma because all art on paper should be behind glass and all oils should not. I have an artist client who paints in oils on 32x40 sheets of mat board he primes with clear acrylic medium. He tapes the mat board down with duct tape to a piece of plywood to make his paintings, So when I get them there are no straight edges and no square sides. He wants no glazing so after squaring them up on my mat-cutter I have been gluing the mat board to cabinet grade 1/2 inch birch veneer plywood with PVA in a cold press and floating them in splined white washed maple frames. Other than some warpage after a gallery varnished one of the paintings, they have held up well. I paint on panels I make in my cold press using rag board glued to dibond, although these are 16 x 20 tops and made before painting. Anyone else ever mount paintings on paper to avoid glass and if so, how?
Baer you're so funny!

Nona et al - I absolutely don't understand every word of the links I post - my technique is to read the introduction and conclusions, and hope for the best in the middle. Think of them as footnotes in my Coles notes musings.

Frank - you're a troublemaker, :D and I'm not going there!

Did anyone read that funny book by Kurt Vonnegut re the abstract expressionist painter's works that just disintegrated? In'challa.

srw19, you don't know this bunch. Someone on a slow day will find an oil artist who wants his just-completed work glazed. Believe me.

This thread---and many others---illustrates once again that the G is one of the more valuable sources of education in our industry.'s fun.
Merpsmom, I wasn't even going to comment on that one, but since you brought it up ... I have four paintings in house right now by the same artist. When the artist brought them in I explained the pros and cons of glazing and they chose to put glass on "the two they are going to keep," but not ont he two they are goign to sell. They felt the buying public was too ignorant and might think it "wasn't real" with glass on it. But the ones they really liked they put glass on. so there srw19

BTW, I am a pastelist myself as you might discover in older threads.
There have been a few refrences on this thread to using conservaion glazing. Does oil paint really fade? I've been under the (mistaken?) impression that it doesn't. If you recommend conservation glazing to a customer, you are implying that it does. Does anyone out there have any information on this? :confused: