Tuesday, August 27, 2013

Silver Stain Experiments pt 1

I've become fixated with the idea of making and controlling my own silver stain. I particularly want to do it following a period recipe to enter into A&S.

[Edit 9/6/13: I'd like to clarify that this "Phase 1" is about finding the right binder. Phase 2, detailed at the end but not well explained, is about finding the right silver and copper compounds to create various colors. Phase 3 is actually using the period recipe.]

After a considerable bit of research I've only been able to track down one recipe, which calls for antimony sulfide and silver in a liquid suspension, diluted 1 part to 6-10 parts by some form of clay (brick dust, ochres, etc). [This book, p. 11]. Antimony sulfide, also called stibnite, is not especially safe since it's an antimony compound. The recipe from that book, incidentally, supposedly comes from one (of many) versions of the Lapidario of Alphonso X (Alphonso the Wise). I've gotten a copy of that specific version, but no English translation is available and automated translations were insufficient for me to pick out the recipe. Fortunately somewhere in my skull is 4 years of Spanish. I am working on translating the document and finding the recipe from this primary source.

A brief aside, I was pointed at the Mappae Clavicula by Master Ali. A latin copy was available and, working with a dictionary, I thought I found another recipe. After I ordered an English translation I discovered a slight error with a big impact. It is still an awesome text with amazing recipes, including many glass-related ones!

Modern silver stain is made using silver nitrate, silver sulfate or (for dark stains) copper sulfate [This book by J. Kenneth Leap] in a binder (various clays or gums will work). For the first round of experimentation I decided to try and make a half-way modern stain to start with, eliminating the least safe part until a later time when I can use a fume hood and better safety equipment.

My "round one" experiment was to use purchased silver nitrate (AgNO3), combined with the binder in the period formula at a ratio from the period formula. I bought two grams of reagent grade silver nitrate online for $10 including shipping [Here]. I ordered yellow and red ochre pigments online as well [Yellow: $6 inc. shipping for 30 grams by Vallejo Pigments; Red: $15 inc shipping for one half-pound of unspecified provenance].

The first step was grinding the silver nitrate. It comes in small crystals in a small amber vial (it's a photosensitive compound, I understand). I used a mortar and pestle, as well as a small disposable brush:

Crushcrushcrush isn't just a song by Paramore...

2 grams yielded considerably more powder than I expected. I used a small-unit digital scale to measure out 2 1-gram portions of the silver. Unfortunately it didn't go further, so I divided each portion into quarters as best I could visually. My primary goal with this was to see if it would even work or if I were missing some other "secret sauce". I then used the scale to measure out grams of ochre to reach the desired strengths. In the spirit of what I'm doing, I mixed the ochre and silver nitrate in a handmade bowl Master Ali ("Arab boy") generously gave me at Pennsic when I went to pick his brain about alchemical implements:

An academic article I found indicated that red and yellow ochres should inhibit the silver ion exchange (for more info, see the Leap book referenced above) that makes silver stain work. The reason is that the iron content in red ochre affects the transfer [Academic article can be found here. For details from it, email me at Brynn dot Herleifsson at gmail dot com]. The article, and several others, was kindly provided by a friend with access to those digital libraries, saving me the considerable expense.

I mixed three batches. The first was mistakenly made weak, 1 part AgNO3 to 16 parts yellow ochre. I decided to keep it and do a 1:16 batch using red ochre. I then made a 1:10 batch using red:

It was a little uncomfortable making lines of various white and colored powders on a digital scale. Just sayin'....

I made small batches of each mix in my usual method (with oil, as I learned from these gentlemen). For a "proper" batch I'd mix it with sandalwood amyris oil, and dilute it for use with lavender. Lavender is lighter, and I wanted the chips to dry faster, so I only used that.

The 1/16 yellow ochre blend, mixed with lavender oil 

The 1/16 red ochre blend, with lavender oil. The 1/10 mix is identical, no photo taken

I put some stain on three test chips and blended them as I normally would. The 1/10 red mix was difficult to blend, but I attribute that to being slightly too dry. My purpose was to see if it would even work, so I moved ahead rather than keep blending (Preparing the chips, the mixing, staining, and starting the kiln were done in the span of my lunch break from work). I used a glass that I've stained before, so I knew it would take without difficulty unless the batch were bad.

The three test chips on whitening, before firing

I fired them at my usual silver stain schedule (also one provided by Williams and Byrne, available here but to summarize.... 212°/hour to 212°, 570°/hour to 1000).

Hours later, I was rewarded:

I've color-corrected this picture to the best of my abilities. The top and right chips are a little too muddy yet, in reality they are just a bit more darker/amber than the other. They also have some residue, detailed below

[Edit 8/28 Afternoon: I have a stronger test chip in the kiln right now, but while walking past my lightbox I realized that a picture taken from an angle shows the color differences between the red and yellow mixes a little better. It's still not perfect, my eyes pick up more differences than my camera:


The un-stained portions are from imprecise handling during blending. The bottom two are the 1/16 mixes, the top the 1/10. Right and top are red ochre, left is yellow ochre.

[Edit 8/29] I decided I needed to try a stronger mix right away, my excitement was distracting. I mixed a 1:6 strength batch with red ochre and fired it today. Unfortunately the results were very disappointing. The chip appears to have even more nasty residue than the others. I'm not sure if red ochre itself makes for a poor binder, or if my particular supplier is unsuitable. I wish I had powder left so that I could try a stronger batch with the yellow ochre, which is the only test chip with no residue. The new one is bottom-right in this picture:

The stain is not brown or amber, there is a hazy shmutz all over the glass, and very little yellow tone. This is the same glass as the other three pieces.]

Lessons Learned and Observations

  • I have one glass palette I use for small batches, tests, etc. I opted for it because I never bothered to sand it. This makes for easier ("more scientific") clean-up and, I hoped, less contamination between mixes. Unfortunately it also made it very difficult to get a good mix!
  • I find alchemy texts and experiments FREAKING COOL. That counts as a lesson learned.
  • I do notice a difference between the red and yellow ochre mixes, however I'm not convinced it isn't due to handling issues. It looks like I got more of the red mixes onto their test pieces, they were quite thick compared to the yellow after I blended them. I will need to try and find a very controlled way to compare them to see if the journal article pans out in practice. This is especially visible in the graininess of the yellow sample above (bottom/left).
  • Red ochre powder is a beautiful substance and a wonderful pigment. It's also a beast to clean up. The chips have what I'd almost swear is fired-in ochre on their surfaces, making them look less clean when viewed close up. I'm not sure what the source is. The palette I used last had "red for flesh" mixed on it, and I had just cleaned it off before mixing the silver stain. The residue looks convincingly like RfF:

A shot of the 1/10 red ochre test chip using reflected light to show the residue on the "inside" (unstained) surface

Next steps

Phase 2 (Sept/Oct) -
  • Try a 1:6 ratio mixture with yellow and red ochres, the strong end of the range given above.
  • Try to keep it very clean and even to compare the effects of the binders
  • Try mixtures with silver sulfate, copper sulfate, and mixes of the three compounds.
  • Try mixtures including brick dust, gamboge gum, and other substances as the binder.

Phase 3 (Nov/Dec) -
  • Try the actual period recipe, involving stibnite (already acquired) and silver
  • Try a syncretic recipe involving a period recipe for nitric acid (aqua fortis) and silver, resulting in a modern formulation made using entirely period techniques (Assuming that they didn't use that same formula, but there doesn't appear to be any existing document indicating as such. The (al)chemical knowledge was completely in place to do so, however). Maybe Roana can use some of the acid for her book binding as well?

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