Friday, February 3, 2017

Silver Stain Experiments Part 2

[Edit: No idea what this is still a draft. Publishing now, three years later!]

Phase 2 has actually turned up some successful blends!

Detailed below are tests I ran with pure silver, silver nitrate, copper sulfate, and silver sulfate as the active compounds. Binders included a new, "brand name" red ochre, yellow ochre, gum arabic, and brick dust. After doing a round of tests I came up with several new ideas, particularly where pure silver and copper sulfate are used, and had to do another set.

Some notes on the binders themselves:

Silver dust and gum arabic - Almost indistinguishable from pure silver dust. Film formed, gum arabic undoubtedly. Weird to see it plainly, but interesting to get a clear visual of the effects of gum arabic. I've noticed recently, when I added too much water to some matting paint, how there is a "thickness" to the water, as you stir the paint you can see some of the unmixed water jiggle and repel the paint until you force it to mix. I've not tried mixing paint with no gum arabic but I think I'll try it to confirm my thought that that is also the GA (rather than the paint). That may be what they refer to as "body" when talking about other binders mixed with water.

Brick dust - Probably needs to be even finer. Works well. I ground pot shards with a pestle and mortar, but I think I need to get it even finer. I'd love to get my hands on a ball mill to do this, but it's not in any shape period.

And a correction from "Part 1" in that I realized I'm slightly blind. As I began to tag and catalog my samples, I almost threw out a few pieces that didn't take. As I was getting ready to toss them I realized that the copper sulfate chip DID stain:

On two slides it's almost imperceptible (this picture above is not a very good example, but it shows up at least) but it was actually there. Because of this realization I tried a stronger mix of copper sulfate for this round. As detailed below in Sample 6 it didn't work out, but I have a good idea why not (temperature).

The stain samples prepared and drying:

A closer shot of the samples:

Silver nitrate and gum arabic made an incredibly pretty, deep orange color while drying. This continued to intensify as it dried, becoming a dark red

The samples after firing:

Sample 1 - Pure silver dust and gum arabic (1:6). Oddly enough, this did nothing. I suspect it takes a higher temperature to work. I know from Leap's book that pure silver leaf will leave a dark amber stain on glass, I can't imagine the powder not having the same effect. Later review of Leap's book indicated he fired his pure-silver tests at 1500°, a full 500° hotter than I did. I know what to try next, and may throw some more of sample 6 in with it.

Sample 2 - Silver nitrate and red ochre (this time from Vallejo pigments). Clear proof that there was an issue with the red ochre I bought before, this name brand sample didn't have the same hazy effect that the first sample left behind, ruining what results there might have been. Part of the sample is a little darker, but I suspect that may be related to how I used it (no blending, possibly imperfectly even surface allowing oxygen to get in, etc) rather than the mix. I consider this one a success!

Sample 3 - Silver nitrate and terracotta dust. A bit of research indicated most of the bricks before the 14th century would have been very similar to what we call terracotta. I bought a small planting pot, smashed it, and started grinding it into a powder. It seems to work quite well, actually. The one downside was that it must be ground very finely. Small "pinholes" are visible in the sample (close-up later in the post). This was caused by less well ground (larger) bits of the terracotta that inhibited the even spread of the silver nitrate. This also left behind a bit of hazing on the edge, but I again suspect it has to do with handling rather than the compound. I also consider this one a success.

Sample 4 - Silver nitrate and gum arabic. Oddly, this didn't work at all. No effect was left behind. Isenberg's book has a chapter on painting and a page on silver stain. It mentions that the "Reddish material" has minerals which pull the sodium out of the glass and allow the silver in. I find it hard to believe, but at the moment have no other explanation for this chip's complete lack of stain. The silver sulfate and copper sulfate chips, both mixed with gum arabic, had visible staining. Silver nitrate did not. The same book also states that "other silver salts" (presumably silver sulfate) are added to stain powders because nitrate is unpredictable and melts unevenly. I haven't seen that to be the case, yet, either.

Sample 5 - Silver nitrate and yellow ochre (vallejo). This mixture was twice as strong as the same combination I tested in "phase 1" and likewise is a much stronger color. This is 1 part silver nitrate to 3 parts ochre.

Sample 6 - Copper sulfate and gum arabic - This is a 1:6 strength mixture, better than what I had previously made. I discovered, just before pitching the last test chip, that copper sulfate actually had stained the glass. The compound was in such a small quantity that it was in the form of tiny specks. I mixed this more strongly and used more of it to try and get a more visible effect. I didn't get it, though again I got visible effects. I think this merits a higher temperature or longer soaking period.

Sample 7 - Silver dust and gum arabic, 1500°
Sample 8 - Silver foil pure, 1500°
Sample 9 - Copper sulfate and gum arabic, 1500°

A close-up of sample 5

 A close-up of sample 3

All 13 test chips I've fired so far

Lesson's Learned

Future Plans ("Phase 3")