To Key or Not to Key...

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MikeGuilbault

MikeGuilbault

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Jul 16, 2011
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ELMVALE, Ontario
as in stretcher frames. I've been hearing pros and cons for both. I'm stretching photographs, sometimes with a mirrored edge for gallery wraps, so the edge of the wrap has to be quite accurate. I understand the advantage of keyed stretchers in the long run, but will a properly joined (glued/v-nailed) not work?
 
I would glue/vnail. I feel it is more secure and the keyed stretchers seem to never stay square. If it is stretched properly you shouldn't have to worry about the canvas loosening.
 
The keys are normally used for a canvas that was stretched prior to painting, to help re-tighten the canvas after it has been stretched by the pressure the painter used while painting. If the canvas is not sagging right after painting, or after the painting is dry, the keys should not ever be needed. BUT, if the painter is using a technique that makes them press hard on the stretched canvas, they will make the canvas sag. The canvas company makes those keys to help expand the stretcher bars to help remove the sag.

If you are stretching a canvas after it was painted, you do not need keys.

All the keys do is slightly expand that stretcher bars, if they are not put in properly, they will shift the canvas out of square, or even possibly crack the paint by over stretching the canvas.

More often than not, you will just throw away the keys.
 
Susan May said:
If you are stretching a canvas after it was painted, you do not need keys.
Click to expand...

I swore I was not going to post on the G again....but could not resist.

Susan, this statement is completely without foundation and is absolutely wrong.

To properly stretch a canvas after it was painted, using a keyable stretcher bar with keys or a mechanical stretcher bar is compulsory.

I refer readers to Paul McFarland's book http://www.amazon.com/Framing-Works-Canvas-Paul-MacFarland/dp/0966318951

or the PPFA Guidelines for framing works of art on canvas,

or- Shameless Plug - I will be teaching Striplining and Stretching Canvas at the PPFA Educational Event in Lake Geneva, WI on April 7-8
 
One trick to keeping a keyed stretcher square is to put a staple in the corner as it will lock the tabs in place. Just remember to have the staple on the back side so you can remove it after you have stretched the canvas an want to key it.
 
I'm not sure if the industry groups have different "terms" but I've always called a keyed frame a "stretcher" and a joined frame a "strainer" in-house so as to easily identify the difference. Inkjet (if you're a bit pompous, "giclee") prints done on a Poly-Cotton mix have not sagged in the 11 years we've been making them, pure cotton ones will sag and will also absorb more moisture and eventually repel the printed surface.

Hornet's nest open...
 
Lance E said:
...I've always called a keyed frame a "stretcher" and a joined frame a "strainer" in-house so as to easily identify the difference.
Click to expand...

And what do you call the structural frame used inside a large thin frame that we call a "strainer"?
 
Well as long as I've stepped in it -

The terminology we have been using in class is:

Stretcher bar stock has a bead. Four pieces of stretcher bar stock that are joined but adjustable make what is called a stretcher bar.

Four pieces of stretcher bar stock that are rigidly joined and not adjustable are called a Strainer Stretcher.

Strainer bar stock is either beveled in one side or flat (S4S). Strainer bar stock is joined to form a Strainer.

Proper stretcher bar stock for stretching inkjet on canvas should have a more rounded bead on both the top and back edge than a stretcher bar intended for canvas.

Dave- the reason I do not advocate using staples in an attempt to hold a stretcher square is that for a tongued stretcher, you are stapling through the tongues and it is possible to split them and to deface the stretcher when removing them. Often more than one staple is required. Large scale keyable stretchers need a more aggressive method of holding true. Mechanical stretchers do not require corner support and that is why I prefer them overall.

The best solution I have found is to use a rigid corner, scaled to the size of the stretcher, that is screwed to the stretcher with the screws set back away from the tongues. I use masonite corners in various sizes that we reuse. Jack Richeson sell them or you can make your own. Some have suggested matboard as an alternative. My experience is that matboard is too flimsy for large pieces and again, I like screws to attach and not staples.

In the case of keys, they need to be trimmed to size and tied off so they will not dislodge and fall into the area between the bead and the back of the canvas. A properly stretched canvas (on keyable bars) will be furnished with 2 keys per corner. Properly inserted, the exposed edge of the key should not be at 90 degrees to the stretcher.

A mechanical bar will have a properly sized shim inserted into the gap created by adjustment and then the drawbolt will be adjusted to hold the shim in place.

All canvas should be properly backed, preferably with a sheet of 4 ply rag and then a sheet of fluted polypropylene. The backing is a part of the canvas and not the framing. If the canvas is removed from the fame, the backing stays with and attached to the stretched canvas. I like truss head lath screws to hold the backing to the stretcher.
 
I was of the understanding the keys were to correct the tension (if required) after aclimation following shipping to a new location, or internal forces in the materials settling. and.. if they're needed, they must be inserted before painting, and be set in place.

After painting (or after a long time). To use any method other than remounting to correct slackness will produce excessive tension in the corner regions. Various conservative groups warn of the dangers of using the keys after painting.

So my real question is. why use keyed or mechanical corners at all if your custom framing for a local client? and not pumping out canvases to ship around the world.
 
Welcome to The G, Jon.
Jon Christos said:
I was of the understanding the keys were to correct the tension (if required) after aclimation following shipping to a new location, or internal forces in the materials settling. and.. if they're needed, they must be inserted before painting, and be set in place.
Click to expand...
Traditionally, the keys are tied, wired, or otherwise secured in their stretcher-bar slots at the time of stretching. Otherwise, an unsecured key could loosen, fall out of its slot, and cause damage from the back of the canvas. However, the keys are not actually needed until re-tensioning (Keying out) is necessary.
Jon Christos said:
...Various conservative groups warn of the dangers of using the keys after painting.
Click to expand...
Could you please refer us to a source for that information? It does not seem to be correct. The whole purpose of "keying out" is to re-tension a painted canvas that has relaxed/loosened over time. The correct process of doing that avoids over-tensioning or damaging the canvas from the back. Incorrect procedure or a careless accident would be the only "dangers" that come to mind.

If stretched on a mitered-corner strainer frame, rather than a keyed-corner stretcher frame, a relaxed/loosened canvas would have to be removed and re-stretched - a much more invasive process than keying out.
 
I have never heard either that you would not be able to use the keys after the canvas is painted on.
I have tightened so many paintings over the years, just by tapping the keys. It is easy, fast and amazing result (in general). I too would like to know what potential problems there would be after painting.

I just had an old oil painting that was completely slack. Fortunately there were good keys. Took me all of 10 minutes to tighten and the canvas looked absolutely amazing. Customer was impressed.
 
I have had lots of stretched canvases that have gone wappy. No prob if it's on keyed bars. Big prob if it
isn't as you have to pull all the staples out and remount it. Even then you don't know if it's going to stay tight.

Big canvas prints that have been stretched on a machine tend to stay taught. One that have been stretched
by hand (particularly by artists) tend to go a bit slack. It's tempting just to chop four bars and underpin them.
It's quick and convenient and you can do any size you like, but it can't be re-tensioned.

Keyed bars allow very fine control as there are eight and they each exert pressure in a different direction/location.

It all depends on the canvas. We tend to say 'canvas' as if it were a universal thing, but not all canvases are
the same. Some will stay tight. Some will expand and flap about. The size of the thing is a big factor also.
 
This is a great article:

Keying Out of Paintings – Canadian Conservation Institute (CCI) Notes 10/9 - Canada.ca

www.canada.ca www.canada.ca

There are proponents of stretching from the corners in to the centre. The opposite of what everyone has learnt. The theory is good, and the tension will be more evenly distributed. albeit a longer and more labour intensive technique as it requires temporary tacking of the canvas while stretching/ adjusting. The classic centre to corners stretching technique concentrates the tension in the corners. This can be observed by tapping on the canvas. If it wobbles largely in the centre like a drum the tension is concentrated across the corners. if it ripples back and forth like a pond surface the tension is well distributed.

Keying out also produces more tension in the corners than the centre of the canvas.
 
The article posted by Jon has some interesting points that not all framers (and artists) are likely aware of.
I know I wasn't.

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Summary​

Stretcher keys (and expansion bolt mechanisms) are appropriate for use by the artist prior to completion of the painting. However, their use long after the creation of the work of art has the potential to cause more serious problems than they set out to solve. The structural appearance of a stretched canvas painting is dictated by the mechanical properties of the component parts (fabric, wood of the stretcher, glue size, ground and paint layers), all of which are affected by ambient RH and temperature. The stiffest layer (or layers) will generally dictate the overall behaviour of the painting. This layer is rarely, if ever, the canvas, especially as the painting ages; it is almost always the glue size.

Tautness in the painting as it is exposed to low RH levels will gradually diminish as the stretcher shrinks slightly and brittle layers undergo stress relaxation over time. As the humidity begins to increase, the stretcher swells and expands and the canvas is pulled slightly tighter. Differences in compression between the centre of the canvas and the outer edges should diminish along with corner draws. However, as a painting ages, the canvas weakens and paint and ground layers lose their resiliency, which makes them susceptible to cracking. Slackness does not always resolve itself. Keying out a painting may appear to be the solution for correcting slackness or local deformations; however, cracking or worsening of cracks, loss of paint and tears along tacking edges will be the result.

If the painting cannot resolve its structural integrity through exposure to mid-range RH levels (40% to 60% RH), then advice and intervention by a professional conservator should be sought. Optimally, display or store paintings where ambient humidity is between 40% to 60% RH and temperature is between 18°C and 24°C. For added protection, or where conditions are not optimal, a backing board and glazing in the frame can buffer the painting from short-term fluctuations in the ambient environment.

Although keying out of paintings is not recommended, loose keys must be secured in order to stabilize stretcher corners and to prevent keys from falling between the stretcher bars and the canvas. Only finger pressure should be used to press in keys, and these should be further secured by methods referred to in CCI Note 10/8 Framing a Painting.

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I hadn't read the cautions in this article regarding keying stretchers anywhere else.
Food for thought.
I do canvas on strainers, only because that was how I was shown.
I've considered switching to stretchers, but now I'm not so sure.:shrug:
 
In my opinion, a lot depends upon the quality of the canvas. If you are using cotton canvas I believe the fixed corners (strainer frame) are acceptable and if you are using a man made canvas (polyester/nylon) then I believe keyed stretcher bar can save you some headaches. Polyester canvas will continue to stretch and you will get waves in it over time if you don't keep tightening it, keyed stretcher bars work nice for this or you may have to un-attach 2 sides to re-stretch the canvas. Cotton canvas will only stretch so far so the fixed corner strainer frame may should work just fine.
 
Interesting article for sure. However, there seems to be no solution of what to do instead, except 'consult a conservation specialist' or something like that.

The quality of the canvas and the paint being used, is always a concern. A lot of paintings on canvas come in unstretched. I always examine the canvas and the paint and warn about potential problem areas. Some canvases might have rips or small holes. Stretching it as is would be impossible. Some paint might not have adhered well to the canvas (both quality of paint and canvas can be issues), so yes, the potential of problems is real.

I am using keyed stretchers exclusively (except for smaller sized where a strainer would be sufficient).

I think the potential danger of removing a painting from the bars and re-stretch it is far higher than using the keys.
Of course you need to know what you're doing and keep an eye on the painting and the canvas itself. I believe that keys are still the safer option overall.
 
Rob Markoff said:
I swore I was not going to post on the G again....but could not resist.

Susan, this statement is completely without foundation and is absolutely wrong.

To properly stretch a canvas after it was painted, using a keyable stretcher bar with keys or a mechanical stretcher bar is compulsory.

I refer readers to Paul McFarland's book http://www.amazon.com/Framing-Works-Canvas-Paul-MacFarland/dp/0966318951

or the PPFA Guidelines for framing works of art on canvas,

or- Shameless Plug - I will be teaching Striplining and Stretching Canvas at the PPFA Educational Event in Lake Geneva, WI on April 7-8
Click to expand...
Thank you. I am very new to this hobby and trying to make a keyed frame for a painting my wife has restored. The book you mention is not currently available and I wonder if you can recommend any other sources of how to fabricate the wood joints for keyed mitres.
 
RogerP said:
...The book you mention is not currently available...
Click to expand...
Paul MacFarland's book, Framing Works of Art On Canvas is available as a PDF download from the PPFA Bookstore for $19.95 US. If you're making stretchers or strainers for canvas artworks, this book will be invaluable.
The PPFA Guidelines for Framing Works of Art On Canvas is another excellent resource.
 
The stretcher system developed by Jimmy LeBron using tight joint fasteners (made for knock--down furniture) is relatively easy and can be done with off the shelf strainer material. Discussions are in the archives.
 
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