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Mirroring stains in sandblasted areas

Hand Lettering topics: Sign Making, Design, Fabrication, Letterheads, Sign Books.

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Kelly Thorson
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Mirroring stains in sandblasted areas

Post by Kelly Thorson »

I coppered a mirror with lots of depth carved areas that I want to gild with gold and variegated leaf. The copper solution has stained the sandblasted areas and I have stripped the mirror right back to glass. No amount of scrubbing and silver strip will remove the darkened areas. Right now I have oven cleaner on it, I'm hoping that may do the trick.
Is there anything else that will remove the darkning? When I go to recopper it I assume I am going to be faced with the same problem. Would it be possible to seal the area with something before I copper it? I know the lye in the copper solutions will lift most paints, but would shellac stand up?
Any ideas would be appreciated, even if they haven't been tested, if you think something would work I'm willing to play guinea pig.
Thanks! :)
I believe there is no shame in failure. Rather, the shame lies in the loss of all the things that might have been, but for the fear of failure.
Doug Bernhardt
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Post by Doug Bernhardt »

What I'd try, and (ain't never messed with the copper) works well with silver is the lye solution in advance of tin and silver. It seems that the aluminum gets trapped in areas that haven't chipped and will tarnish...what I've also noticed is the tin doesn't seem wash out thoroughly enuf on occassion with similar results. It would be good to actually see the problem but there's a stab at it.
Sarah King
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Post by Sarah King »

Kelly,

Mike, the chemist, says that oven cleaner probably won't work since it is alkaline so it won't dissolve the metal. If you have some nitric acid, you could try leaving that sit on the glass for a few hours. Of course, clean off all the oven cleaner first and scrub the glass well. Then you only need as much nitric acid as will fill the carved areas. Wear golves and all that good stuff.

I'm pretty sure that the way to avoid the problem in the future is to block the tin and palladium from depositing on the glass. I did some experiments in reponse to a customer's questions and I know that if you tin the glass but don't apply the palladium sensitizer before you pour the copper, the copper mirror doesn't form at all. All you get is an unlovely pink haze on the glass. You can easily block the tin and palladium with shellac or rubber cement or vinyl or even wax. What you use would depend on what you want to do with the area after you mirror it. I like the idea of rubber cement but I haven't personally tried removing it from sand blasted glass.

I can see more experiments coming up. We have a few ideas for a simple to use copper remover that's less toxic than silver strip, but need to make a few purchases first. We'll keep you posted.

Sarah
Sarah King
AngelGilding.com
Kelly Thorson
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Post by Kelly Thorson »

Thanks Doug and Sarah,

The staining looked like it was just copper initially but ended up looking quite black after using the silver strip on it.

The oven cleaner seemed to be a bust, but after using it I cleaned the glass well and took more silver strip to it and this time it worked. I don't know if it has anything to do with the sodium hydroxide (isn't that lye?) in the cleaner or just the fifth attempt at silver strip...in any case it is clean now. I had initially used lye (Drano) to clean the glass as I blasted with aluminum oxide.

I coated the depth carved areas with shellac and will try and see if that will work. The problem is if I copper it again and end up with the same staining, I don't know how to get rid of it without damaging the backed up areas. I think you have the solution with not masking the tin and pallidium sensitizer Sarah, but because this has been previously tinned and sensitized, will it make a difference, or does the stripper take all that off as well?

I'd be really concerned with the idea of using wax as I have seen how the copper eats the wax on paper cups. I'd think it would attack the wax and you'd end up with wax "floaters" all over the place. What do you think?
I believe there is no shame in failure. Rather, the shame lies in the loss of all the things that might have been, but for the fear of failure.
Sarah King
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Post by Sarah King »

Well, I love experiments. I tried deep blasting (1/32"??) on a small bevel and filling the areas with Ross No Wrinkle Rubber Cement and then pulling the mask after a minute or two. The mask pulled off the extra rubber cement and left nice clean lines. I copper mirrored the piece. The copper stayed out of all of the rubber cement areas leaving them nice and clear. The rubber cement did not lift at all. When the mirror was done, I was able to rub the rubber cement (haha) out of the sand blasting with the mid section (the hard paper part) of a Q-tip.

I would say that the experiment was a complete success except that the copper developed little bubbles and so some washed off when I rinsed it. Since it has done this before without the rubber cement, I'll have to do further experiments to see if the rubber cement is the culprit - and whether I should have left it to dry longer. I get too impatient. - On further examination, I notice that the areas where the copper lifted were not next the the rubber cement but at the edges. Clean your glass, girl!!

About the tin and palladium - in my experience, the silver strip remove tin and palladium entirely so you are back to clean glass. I don't know why the oven cleaner helped the silver strip. I was thinking that you could mix a little glass cleaner with the silver strip since it contains a wetting agent that destroys surface tension and lets the strip contact the glass more closely - the same principal as adding dish soap to glass size.

It's my bet that the shellac will work just as well as rubber cement. I'll be very interested to hear how it comes out. I tried rubber cement because its so easy to remove later.

But what fun it is!! keep us posted.
Sarah King
AngelGilding.com
Sarah King
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Post by Sarah King »

I forgot, Kelly. You're right about the wax of course. Not a good idea.
Sarah King
AngelGilding.com
Russ McMullin
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Post by Russ McMullin »

I'm having a similar issue. Kelly wanted me to send her some pictures of the piece I was working on at Larry's. She wanted to see the texture in the letters. When I pulled it out, I noticed how the mirrored areas were tarnished. At the meet we had tried angel gilding first, but didn't get a good mirror so we put copper on top. We didn't have a chamois to wipe off the crud layer that the copper leaves so I just washed it off the best I could. Apparently it wasn't good enough.

I used laquer thinner and an old oil painting fitch to get the backup paint off. Silver strip took most of the gold and copper off, but there is still a stain in the sandblasted areas.

Image
Image

Now that the glass is dry I can see some slight residue in the blasted areas. It has a very light copper tint to it if the light is just right. Otherwise it looks bluish gray.
Sarah King
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Post by Sarah King »

Russ,

I don't think the copper tarnished because we didn't use a chamois to remove the crud. I'm begining to think that it tarnishes because of adding One Shot hardener to the paint. Larry and I have both had problems with the copper tarnishing after it's been "leathered" as they say. Do you know if your paint had hardener in it?

As to the copper stains in the sandblasted area, you could try nitric acid if you have any. If you're willing to wait for a week or two, we are working on a copper dissolver that might work better than silver strip.
Sarah King
AngelGilding.com
Russ McMullin
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Post by Russ McMullin »

The backup paint did have hardner in it Sarah. Unfortunately I don't have any nitric acid handy. If I can't clean the glass some other way, I'll wait for the product you are making.

Oh, I should mention that I've got your pictures ready to send, probably tomorrow.
Kelly Thorson
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Post by Kelly Thorson »

Russ's pictures are pretty much exactly what I was faced with. The deeper etched areas were like the Dickenson letters. The less blasted areas were similar to the larger letters. The blasting at Larry's wasn't aluminum oxide so I don't think that is the problem. I've noticed that gold is hard to get off in blasted areas too, but nothing like the copper.
I believe there is no shame in failure. Rather, the shame lies in the loss of all the things that might have been, but for the fear of failure.
Sarah King
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Post by Sarah King »

Thanks for the info, Russ. I'm very sorry your piece went bad. It's a real bummer but at least we know now that the hardener is the problem. When I first noticed this problem on my glass samples last September, I did up some test pieces and they have been sitting with their backs to the sun since then. So far the ones backed with Black Permalac, Clear Permalac, One Shot Clear Acrylic Spray, asphaltum and Sericol Fast Dry Black Enamel thinned with napthpa are all fine - no fading or tarnishing. The control piece was left with no backing and it has faded very slightly. The one backed with clear spray shellac has faded a lot, but not tarnished.

Using hardener in the paint is great if you need to scrub off gold leaf and dried gelatin size, but you don't need it with mirrors which can be chemically removed with Silver Strip (except on sandblasted glass, it seems). Looks like the way the metal is stuck on the glass determines what paint you need to use to keep it there. I'm sorry you had to be the one to confirm it.
Sarah King
AngelGilding.com
Robin Sharrard
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Post by Robin Sharrard »

Hey Russ, the upside to this (for someone out there...) is you got a realy neat antique effect! Too bad you have to wast so much material to get it. It realy brings out the "Mica/acid" etch over the sandblasted areas, and it looks like you airbrushed a dark shadow around the depth carved letters. Robin
Robin Sharrard
Sharrard Graphics & Signs
Fallon,Nevada
Ron Percell
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Post by Ron Percell »

Try alcohol
Sarah King
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Post by Sarah King »

Ron,

I tried alcohol and it didn't make any difference to the copper at all. I'd love to know if this is a technique used on gold leaf - does it dissolve the size?
Sarah King
AngelGilding.com
Kelly Thorson
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Post by Kelly Thorson »

Shellac is not the answer. :lol:
The lye in the copper lifted it and made a mess.
Now I get to clean out those blasted blasted areas again. :roll:
I believe there is no shame in failure. Rather, the shame lies in the loss of all the things that might have been, but for the fear of failure.
Ron Percell
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Post by Ron Percell »

The alcolhol is just a step through base chemicals.

Alcolhol added to water size, accellerates dry time and helps reduce snail trails from gelatin deposits, use less than 5% and work fast.
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