"cloudy" acid etch

cam bortz · Post by **cam bortz** » Tue Nov 01, 2005 9:27 am

I'm working on my first couple of acid etch pieces, and have run into an issue - on one piece, portions of the areas that were etched have a milky or cloudy appearance. On the other piece the etched areas were quite clean and bright. I had gilded both pieces on different days with seperate water-size mixes, and noticed the cloudiness in the gild behind the etch. Thinking this was a size problem, I scrubbed off the gold and re-cleaned the glass, but I can now see that the cloudiness is in the etch, not in the gild. I've cleaned and re-cleaned, using glass cleaner, bon ami, ammonia, and clear grain alcohol, (just about everything I can think of ) but the cloudy areas remain. The glass outside the etched area is absolutely clear, as are other parts of the etch.

Any suggestions?

Larry White · Post by **Larry White** » Tue Nov 01, 2005 10:14 am

Hmmm.... That can be caused by a few different things. I am presuming that you're refering to mica etching. Did you follow the directions for mica etching as posted on the Letterhead site? ...It could be a time versus acid strength issue. If the acid is left on the glass to long, the glass that has been eaten away can re-attach itself to the glass resulting in a cloudy gild. I've also seen this occur if the mixture is at a uniform thickness over the etch areas. Also, if the mixture has been used over and over (not your case evidently), it can produce a more subtle texture and/or fogging.
Hope that helps. Perhap Pat M. can chime in.

-LW

cam bortz · Post by **cam bortz** » Tue Nov 01, 2005 4:41 pm

The glass was etched at Jeff Lang's a coupla weeks ago; we did a bunch of pieces at various times over the weekend. I just gilded another piece from that session and it came up perfect. Because I didn't gild it right away I can't say if the cloudiness was there from the start.

Since etching the glass I glue-chipped other areas of the same piece, using a mask resist instead of asphaltum (which worked fine, btw) . The area that was etched was completely masked over, so it had nothing to do with the sandblasting or chipping, so far as I can tell.
the cloudiness is very subtle and does not cover the entire etched area, only portions of some letters, but really shows up when gilded - it looks like a cloudy gild. I might have suspected some sort of residue from the mask, but it does not respond to scrubbing.

I'm going to try gilding a small area again and see how it looks.

Larry White · Post by **Larry White** » Tue Nov 01, 2005 6:23 pm

It's most likely in the glass and can not be removed. You could just proceed and chalk it up to "character" of the piece. After about 5 years, you probably won't even notice it any more.

-LW

Patrick Mackle · Post by **Patrick Mackle** » Wed Nov 02, 2005 11:17 pm

A cloudy or non bright mica etch could be the result of:
-not enough fluid acid in the mica mixture resulting in the mica retaining the acid away from the glass, while allowing the acid to "fume" the surface more than bite into the surface. On the other hand, to much acid could impair the protective close contact action of the mica flakes and allow the acid to form its characteristic flourosilic micro sized crystals into the glass. When rinsed with clean water, these flourosilic crystals dissolve out of the glass surface leaving micro imprints of those crystals like little fossils. These micro structures appear as a matt finish. There is a possibility that etching on the tin side of glass could dramatize this problem.

While reproducing acid etched windows for the original 1934 Queen Mary. I noticed that the mica etched areas were noticably deeper than I had generally seen before. In an effort to duplicate the broken originals exactly,
I attempted to do double mica applications in those areas. The outcome was exact, resulting in a deeper and crisp dense mica texture.
You might try applying another mica etch to the cloudy mica section.
Pat