Museum glass chemistry?

[Mike LeCompte CPF]

not to steal Doug's thread: customer asked how do they make Museum SO very "not there"? We have several samples on the wall, sell it quite a bit, but no on eever asked that question.

Answers? How is it made so it's so transparent? Should know but don't

 

[Jim Miller]

Hugh Phibbs, who is directly connected with scientific experts, such as conservators employed by our federal government, probably knows more about the nature of the metallic coatings than anyone else on The G.

The coatings and the process of applying them are highly proprietary details. At least, that's what Tru-Vue said when I asked.

 

[Doug Gemmell]

I'm with you Mike I should know but don't. Hopefully your question will change that. I've heard everything from it has less iron content than regular glass to it is a coating they apply. Don't know how you can add something to something to make it less but anything's possible these days. And this is NOT directed at Jim. I've heard the coating reason from others. It could be a coating!

Hey, I got through a post without ripping museum!

Mike, what do you mean "...it's not there"? Look for the stupid green ripples!

Sorry, I can't help myself.

 

[JohnR]

The trick is in the anti-reflective coatings. These are used on camera and eyeglass lenses as well. This link describes the process:
http://www.canon.com/technology/s_labo/light/003/03.html
John

 

[Baer Charlton]

Thanks John, Some days you just want to . .

Next week at PMA, I'm sure there will be a Tru Vue rep sitting there saying "It's highly proprietary", and hopefully the Nikon booth is next door with the display that they had two years ago that explained how the Anti-reflective coat worked and how it was done and what was in it.

We all have customers that think we are "wizards performing magic"... but I wouldn't tell them that I use a magic wand to cut mats....

 

[JohnR]

Baer,
I thought a Wizard performing magic was a type of CMC?

John

 

[Jim Miller]

Originally posted by Baer Charlton:
Next week at PMA, I'm sure there will be a Tru Vue rep sitting there saying "It's highly proprietary"...

I'm sure you're right about that, Baer.

At the beginning of the huge machine that applies the AR coatings, there's a little room where the coatings are mixed and piped into the machine. That room has one door, and it is locked. When touring the Tru-Vue plant, that is the one place nobody ever gets to go.

If Tru-Vue won't tell us how they make their anti-reflection glass products, perhaps Denglas will tell us how they make theirs. Right? Isn't their product proprietary, as well?

 

[Baer Charlton]

As is OptiCal, View Perfect, Shooters, and Optical Coatings.

And that puts them all right up there with Bushes Baked Beans. Or Hilla Beans.

Explaining HOW the coating works, is not the same as revealing the recipe.

 

[Doug Gemmell]

I got the anti-reflective coating on my reading glasses. They have a slight blue reflection. Don't know who manufactured the lenses but the point is, why is one company secretive about the coating material when so many others obviously use same or similar?

Not slamming museum glass,(this time) just wondering.

 

[JohnR]

Doug,
They may have engineered a way to apply the coating quickly and at a low cost. That is what their secret may be.
John

 

[Jim Miller]

Originally posted by Doug Gemmell:
...why is one company secretive about the coating material when so many others obviously use same or similar?

One company secretive? Is there any maker that is NOT secretive about their optical coatings for framing glass? If so, who is it and what information do they offer?

It seems that all of the makers have developed their own proprietary chemistry and application methods. They may be similar, but who knows?

Maybe a larger question is: Who cares? Why would the manufacturing details matter? Protective qualities matter, of course, but light spectrum test data is generally published and pretty easily verified.

Regarding visual qualities, should anyone choose glazing on a basis other than appearance? That is, if your customer prefers the look of brand A, and mine prefers the look of brand B, would either of them change their minds if one of the makers revealed their chemistry?

 

[preservator]

Anti-reflective coatings work by altering the
light so that ougoing reflections are made opposite in phase to incoming light, canceling
the reflection. These coatings are usually oxides
of titanium and silicates, none of which has
any chemical implications for the material in the
frame. The anti-reflective effect is limited to
about 60 degrees from the plane of the lite, so
it will not work, when seen at an oblique angle,
or for reflections of the light source, itself.

Hugh

 

[Doug Gemmell]

Mike's question was "How do they make it so transparent?"

Is it the anit-reflective material that achieves this or something else?

Reflection aside, it does seem to be clearer than regular glass. Is museum glass regular glass with AR and UV coatings?

 

[preservator]

Check with the maker, but a premium product like this is probably made with low-iron (water white)
glass (substrate).


Hugh

 

[Jeff Rodier]

The Grumbler by the name THE GLASSMAN explains the different types and manufacturers in this link. He might even have the chemistry answers that are sought.

http://www.thegrumble.com/ubb/ultimatebb.php?ubb=get_topic;f=1;t=009964#000014

 

[Doug Gemmell]

Glassman says museum's substrate is Guardian Extra Clear which has improved transmission and reduced coloration.

Thanks Jeff. The more we know about the products we sell the better!

 

[Jeff Rodier]

The Glassman has been very helpful in clearing up our glazing questions in the limited number of threads he has participated in. The combined knowledge in this place is mindblowing.

 

[the glassman]

Hi .. and thanks for the kind comments on my miserly efforts at posting.

TruVue (and others) use a standard and widely known process for their AR coatings (on Museum, AR and Perfect Vue glasses). The process is known as Optical Interference Coating and consists of multiple layers of metallic oxides which selectively alter the refractive index and therefore the light transmission characteristics of the glass substrate. There are (as far as picture glass goes) 2 methods of applying the coatings: 1) by dipping the glass into successive baths of the various oxides in solution with a bake/cure process in-between each bath (Denglas and Schott) or 2) by passing the glass several times through a sputter-coating machine which applies the same layers by means of a positive-negative charge process.This machine is also known as a Magnetron. (TruVue, Flabeg,Luxar)
In practical terms there is little difference between the glass produced as long as the actual glass substrates are the same. Some users claim that the dip-coat process gives a smoother, easier-to-clean surface - and there may be some truth in that.

TruVue use (to the best of my current info) Guardian's Extra-Clear substrate, which will filter more UV than a true low-iron (or water-white) glass and so allow them to hit their UV numbers and offer a low-reflectance (AR) UV product with Museum Glass.
Museum Glass is no more than Conservation Clear with the AR coatings applied on top. The UV coating is rather obvious (rippled) on Con Clear and even more so when under the AR coatings of Museum Glass. It also reduces visible light transmision. You could not get to see the AR process during a trip to TruVue in Chicago becaue the process is done in Minnesota.
The Denglas/Schott process has to be carried out in fully enclosed conditions and is therefore not very spectator-friendly.

The "Holy Grail" is a true water-white float glass with an invisible 99%+ UV filter and optical interference (AR) coatings. Until then, it's Museum or a WW/AR Laminate - according to you budget!

Optical Interference coating and allied coating processes are very widely used in all manner of industrial and scientific and optical applications. Without them you wouldn't have the photocopiers/TV's/Scanners/Spectacles/binoculars/etc. etc. that rely on modern coating technologies.

.... yet another posting to help insomniac framers get off to sleep!

All the best from UK