Chalcedony/Schmaltz Random Notes
As I find them again , I'll post links here that relate:
As a part of the purity issue, I know from experience that both bottles and plate make great schmaltz and really high purity batches do not. Mess up your really clean batch with some iron and it works much better. The small amount of sulfur left from adding salt cake (sodium sulfate) also adds a lot to this result.
I too could not find the reference in Scholes, but I have reread parts of that book many times before finding what I needed to be looking for.
The first times I really made silver Schmaltz glasses, I was still melting plate glass. It was about 1970. The opalizing came very readily and it took me a while to realize it was because of all that iron in the plate glass. Without the iron, silver opals are problematic at best. With it, it's pretty easy stuff to make. Remember what I said about iron in that other thread on crucibles. in your gloryhole.
I have made calcedonia's in cullet in the past but it is difficult in a cullet that is oxidizing in nature. In about eight pounds of actual glass, I would recommend adding 4.6 grams of silver nitrate, 28 grams of zinc oxide and 28 grams of black tin. Then add two grams of red iron which is key to success in this glass. The iron allows for nucleation points in the glass ( places where crystals or colloids like to form). Melt the glass kind of cold- about 2180F. Melt in a neutral environment. When you gather it, allow the gather to really cool down and then reheat it hard in the gloryhole. If it is going to strike, that will make it happen. Repeated heats intensify the color.
My belief is that it has to do with the melt temperature. Silver glasses form what are known as colloidal suspensions which are essentially big molecules in long strings. If you melt cold in a neutral atmosphere (2200) the glass is usually transparent on gather ing and if allowed to really cool down and then be heated hard, the collodial activity gets going. Those big molecules reflect light right back at you.
If melted to hot, I think (think, mind you), the molecules tend to be much smaller in overall size. I don't think they are necessarily shorter. The smaller ones don't reflect light as well. Further, the silver goes more into solution at higher temperatures. The black tin tends to create a really good environment for the molecules to form, particularly if in the presence of iron, which is a multivalent metal. It allows those molecules to form easily.
Industry hates the stuff because it is so wildly unpredictable. I melt this stuff and then suddenly will lose the capacity to melt it well for weeks on end and have no real hard information as to why it gets lost. I do know that the iron is critical to it sticking around. Zinc is also a great additive to silver melts. Too much silver makes the effect decrease, not increase.
That would be a cullet with about 12 grams silver nitrate in 21 lbs of cullet plus 60 grams of black tin and about 20 grams of Ferrous oxide ( red iron). It may take more silver depending on the state of oxidation in the cullet.
* In spruce pine, add about 12 grams of silver nitrate to 20 lbs of SP 87. Also add about 15 grams of red iron, 20 grams of black tin, 20 grams of zinc oxide. It tends to be a little brown using SP. The iron is really important.
If you want it to be a luster glass, take the silver up to about 35 grams. You will also need to add 35 grams of silica to it at this point or it won't fit. Pete V
* At twelve grams you should not have a fit problem, although 10 grams of silica in that mix will give you a perfect fit. Save your SP87 bags that didn't pelletize at all for doing this. If it comes out too light, increase the black tin. You are fighting nitrates in the mix which I hadn't though of before. You can buy the color base from Tom without the nitrates. It tends to be more brown than yellow, I like the yellow.. The swirls you describe will be there. Slight reduction is fine. 10 grams of table salt won't hurt either. Pete V
1/8 % silver (.125%)
3/4 - 1/2 % copper (.75 to .5 %)
1/10 % sugar (.1%)
1/4 % cobalt when it works (.25%)
Decrease calcium and magnesium
Increase zinc and Barium
And it is not actually a silver schmaltz. It has no black tin in it so it is a veiled translucent.
It isn't basic stuff at all. Silver glasses are so unreliable that industry avoids them entirely.
How much silver nitrate per lb are you adding? My most recent silver opal blue batch in the furnace right now had 2 grams of cobalt per lb on top of the silver opal base which had .43 grams silver per lb of batch. The tin content was .35 grams per lb. I had an equal amount of Zinc.
The color develops on reheating and I believe that the opacification occurs as colloidal molecules of the silver compounds grow . These are enhanced by iron oxide which has a multivalent role in the glass and provides a point where the molecules can start to grow. Chuck always called these nucleation points. I find the iron to be really helpful.
So, check your silver content, add a little red iron and increase your cobalt.
Hey Dave, try some TiO instead of iron (say .7g per 50lb) It will take longer to strike opal and you will get a wider, more controllable (with heating and cooling) range of color. The Ti is a much smaller seed than the iron. It also stays less brown when it goes opal. If you nail the black tin/sugar% you can have a glass that plates silver (a trait of a oxidising body) or opalizes (a reducing body) (I guess it would make it a N to slightly O- body) depending how you treat it. A small window that would probably be hard to deal with with knockoff as you have no way to keep things consistant. (But doable with a known feedstock like 101SFS)
well, it can be made badly. It's really easy and tempting to use too much silver. I make it up now, frit and crush and then roll it onto other colored opal silver glasses. That has some really nice effects. When we were coaxing the color at Simpson's in that Corona glass I formulated , we would take an oxy acetylene torch and hit the surface of the pot wit pure acetylene for 30 seconds before the slap gathers. That certainly woke it up.
But if you want to use it as a heavy draw glass for a production shop, It's going to disappoint you. It will turn grey. It always does. I used to tell Simpson that if he wanted to really make the corona work, he would need at least four pots of it and the draw would have to be distributed between them. There are reasons.
Silver glasses are known as fugitives for a reason.
If it gets gathered, it's getting mixed given the rotation of the blowpipe. The top one inch is where the action always is since it's a complete interaction with the furnace atmosphere. That was my inference when I talked about the acetylene torch. It indeed wakes it up.
The net effect of stirring ( gathering) turns it grey. If you try to do production, you will turn it grey. It's why I told Simpson he would need multiple pots of the stuff and to rotate from pot to pot if he wanted to keep the color working well, even with the torch. A slap gather, where you let an existing parison down into the pot on one side, and you don't turn the gather at all really lets the color jump. You aren't rotating. It takes a certain amount of skill to blow that sort of thing out evenly.
Calcedonia is a color I have been working on for the last month at Josh's. Dino Rosin once told me mine was the best he had ever seen, next to his of course. I am doing one which has a peach blush. I have made calcedonia's in cullet in the past but it is difficult in a cullet that is oxidizing in nature. In about eight pounds of actual glass, I would recommend adding 4.6 grams of silver nitrate, 28 grams of zinc oxide and 28 grams of black tin. Then add two grams of red iron which is key to success in this glass. The iron allows for nucleation points in the glass ( places where crystals or colloids like to form). Melt the glass kind of cold- about 2180F. Melt in a neutral environment. When you gather it, allow the gather to really cool down and then reheat it hard in the gloryhole. If it is going to strike, that will make it happen. Repeated heats intensify the color.
Too much tin makes this stuff brown out . Same to be said about too much silver. It's a touchy feely glass and is notoriously unreliable which is a lot why industry doesn't try to use the color. I do make color rod of it in a 96 but it is a happier glass in a pot. It also performs better if you slap on the gather instead of rotating in the pot which reduces its effectiveness.
Eben, that is too bad about the notes. Can I help with any of that?
10 lbs batch
4.6 grams silver nitrate
28 grams zinc oxide
28 grams black tin oxide
2 grams red iron
melt cold 2150-2175
The time to melt and fine ( I hate the term "Cook") really varies from furnace to furnace. It's slow to fine without borax.
Take note that the silver is in tenths of a gram and deviation on that makes a big difference. It's a powerful colorant. You can also note that the stuff I posted for last week had the same additives but used 8 lbs of cullet. Thats the rough part of the C02 loss.
I did melt this in SP a number of years back and firstly, you had to use the colorbase, not the regular oxidized batch or you didn't show color at all. When I did use it, it muddied up somewhat brown and I didn't pursue it. I did suspect the feldspar at the time which was a kona F4 if I recall correctly. The batch I worked for Josh was ( ahem) cheap. It was a soda glass with some borax in it to reduce viscosity. We used regular whiting, and did use that kona spar again. I needed to use materials that Tom keeps in stock at Spruce Pine since he did the mixing as tonnage once I provided the formulation.
And remember that the colorbase from tom needs to be mixed when you get it. It's not premixed like SP87 is.
I hope that helps.
I am always glad to run into people who actually are following in the path. I certainly learned at the feet of Dudley Gibberson, Mark Peiser and Chuck Savoie. It seems to me that glass workers suffer from a periodic loss of all useful information about every eighty years, mostly because people believed they had to be secretive. It gives me a lot of pleasure to see people actually trying some of this stuff instead of continuing to believe that it can't be done or is way too costly to do ( it's actually much cheaper than color rods) or just too scary to do.
try adding four or five grams of red copper.
Salt does interesting things too.
If it is browning out, back off on the silver by a few tenths of a gram.
from 1972 westwood glass catalog
A small amount added to batch makes a bright yellow
In reduction this becomes opaque colors
3/4% silver nitrate plus 1/2 % stannous chloride = chalcedony...suggest dissolving the nitrate in water for better distribution in the batch.
Art is not a thing...it's a way.
Last edited by Dave Bross; 12-20-2016 at 08:28 PM.