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Old 12-01-2018, 03:09 PM
Bradley Howes Bradley Howes is offline
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Black Calcedony

Hello All,

I've been using a modified version of Pete's calcedony to do some research into calcedony. I'm currently an undergrad at Alfred University with Angus Powers as my teacher. I'm taking Glass Art Engine, a class that brings artists and engineers together to find 'problems' in glass that we want to work on.
For those who don't know, Pete's calcedony is:
8 lbs cullet
4.6g silver nitrate
28g black tin oxide
28g zinc oxide
2g red iron

I'm using 75% of the silver, 7g red copper oxide, and about 100g sugar for some reduction.
About 50% of the time, the glass is black with a few cords of color. My very first run of calcedony looked like it was dipped right out of one of Josh Simpson's crucibles. When it turns out black, I'll weigh out about 25% more oxides and throw that on top of the pot and mix it in with a punty. After 30-60 mins, the glass is a lot better but still not great.
I understand calcedony is a fickle color but I'd like to know if there's anything I can do to influence it in future melts.
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Old 12-01-2018, 03:35 PM
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Pete VanderLaan Pete VanderLaan is offline
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I've read this twice. I can't even figure out what you want it to do.
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Old 12-01-2018, 04:55 PM
Bradley Howes Bradley Howes is offline
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So a couple times, it turns out great (vibrant blues with lots of swirls and other colors as well) and I won't have to do anything to it. About half the time though, it just looks black with a few streaks of color. Mainly I want to understand what could be causing this.
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Old 12-01-2018, 04:56 PM
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Pete VanderLaan Pete VanderLaan is offline
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I've let this gnaw on me for about 45 minutes while watching Rachel Maddow summarize the Trump scandal. That let me distill some stuff from this question and here it is:

You start with "cullet". If it is anything commercial it is several things, first, cheap as it can be. Secondly it will invariably be an oxidizing cullet meaning it has a lot of O2 drifting about in it. Some is indeed driven off in the initial melt but the fingerprints remain.
I don't start that way. I make a glass batch which is devoid of as much O2 as I can pull off. Then. I liberally shower it with items you mention- black tin and zinc.
Then you go off and add a LOT of red iron. Then, you cut the silver. My experience with the iron is that it is a nucleation point for crystals and colloids to form due to the valence issues with iron. Too much in my experience is not a good thing. I wrote it after virtually years of trial and error. I'm currently in year 48, I think,.

Then you seemingly substitute sugar, I don't know why but it would make black for a while. It's not something I would have pursued. You might as well add silicon carbide.
Josh Simpson's makes a cheap manganese black which always shows black when it's thick enough. Purple when thin. It contains cobalt as well. For me, Black is black all the way down to the finest powder and mine looks like coal dust. I have the Simpson formula in my files from the time I was deriving the glass he now uses in those Corona platters, I have a whole notebook on the things I did to those glasses but, there was never a cullet to start with. What I did do, was to reverse engineer the Louis cullet for viscosity and expansion and then modified it. Josh wanted it mixed at Spruce Pine which I told him would not work. What they send back was a mismatch and I won't go in to why that occurred here. Suffice it to say I knew why it would not work beforehand.

Anytime you are making those type glasses, you have to consider that there are local conditions in the glass and that there are atmospheric conditions as well. Chalcedonia's are not happy with the interface. You can make only so many hot pieces with those glass bodies before the conflict begins. I told him at the time that to do production of the platters was going to take multiple furnaces all being ready for short campaigns.

But , you want to turn it black. For me, black is black absorbing all light. How is it possible to make a glass that shows almost every color in the rainbow in the best calcedonia "Black"?

Buy some books. There are a number out there with formulas. They are roadmaps if you can read them. Helmer, Thuringen , Weyl, Volf. Then, get rid of the statement you make at the bottom of your post until you actually deserve to make it. I try my best every day but I don't talk that way.
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Old 12-01-2018, 09:11 PM
bob gent bob gent is offline
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You mention books with color formulas. Could you name a couple?
I once bought Weyl and had a few recipes that I was told came from Penland and called for SPB color base. I got me a couple hundred pounds of color base and some chemicals intending to try a few colors. My kids were born shortly after that, and my (now ex) wife pitched the Weyl for me (it's okay, I didn't understand it well enough anyway)
What I'm left with all these years later is all that SPB color base and a bunch of dangerous chemicals that would be better used in glass. I'd love to make a little color pot and go back to trying out color formulas
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Old 12-02-2018, 08:05 AM
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Pete VanderLaan Pete VanderLaan is offline
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Quote:
Originally Posted by bob gent View Post
You mention books with color formulas. Could you name a couple?
I once bought Weyl and had a few recipes that I was told came from Penland and called for SPB color base. I got me a couple hundred pounds of color base and some chemicals intending to try a few colors. My kids were born shortly after that, and my (now ex) wife pitched the Weyl for me (it's okay, I didn't understand it well enough anyway)
What I'm left with all these years later is all that SPB color base and a bunch of dangerous chemicals that would be better used in glass. I'd love to make a little color pot and go back to trying out color formulas
Helmer, Henry : Secret batch book
Lynngard, Finn: Thuringen recipes
Weyl is not a recipe book. It's a roadmap. That's true of Volf as well.

Helmer is still in print, The Thuringen book is not at this point. Joe Pfeiffer had some copies of it that he bought from Finn's widow. I do not know if he was able to get rights to reprint. Helmer was a remarkable man, largely unsung and that book is also out of Joe's group. His studio is Igneous glass and is based in Utah. You should be able to use the search function here to learn more on that. In general, the search function here will lead you to a lot more formula information from back during a time when I was more forthcoming. These days I've become more like Frederick Carder about it. You can always visit the Rakow in Corning and you'll find lots of information there.
Your SP color base was developed in my first color class and Tom Littleton went home to mix it. It does not have any nitrates or antimony in it, an important omission of you want to make copper ruby and silver glasses. It is not mixed however. It's just dumped in the bag in the right proportions. We sell 7lb crucibles for melting and they can be had elsewhere as well. SP makes copper colors poorly in my estimation but they are indeed red. Colloidal glasses do best with different alkaline fluxes.
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Old 12-02-2018, 08:24 AM
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Pete VanderLaan Pete VanderLaan is offline
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100 grams of anything added to 8 lbs of cullet is a massive addition. All you're doing is making the glass reduce- short term and it goes away. Kiss your expansion goodbye . You have changed the silver content substantially and the tin was already supplying the reducing conditions but you are fighting a cullet. The last time I went through this and swore it off, I asked an individual a simple question and said "what color is your black Tin?" "He said "white"

Beyond that, I haven't used that formulation in light years and I change and adapt. If you are indeed in a class at Alfred trying to learn about certain glasses, you should do the melts changing one item at a time. Perhaps better for a masters degree.

My success is based in my actual clear formula ( I have seven actually) supplemented by tons of test melts. It too gets modified as time goes by. That alone should tell you this isn't static. I just spent the last year, or close to it teaching about color making with only one student. I was continually amazed at the things I left out of explanations that became problems immediately. I made too many assumptions. So, these days, I prefer watching as enthusiasts figure it out.
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Old 12-01-2018, 09:32 PM
Bradley Howes Bradley Howes is offline
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For the statement at the bottom of my post, I wrote that when I was younger, stupid, and very arrogant. I can only hope I've gotten less stupid and arrogant since.

Having written this post, please bear with me as I ask a ton of questions in this. I'm trying to soak up as much knowledge as I can.

I've done this recipe with two different cullets. One was East Bay Batch Electric, a melt produced by East Bay Batch in the SF Bay Area for electric furnaces, the other was Spruce Pine (not color base). Both times, glass was ladled from the furnace into some water to frit it.
When you say you shower the glass with tin and zinc, is this in general or when batching calcedony? The amount of iron I used was found on a post you wrote, I think it was from 2011. What are the valency issues you're referring to with the iron? What has your experience been with changing the amount of silver? Do you get a better calcedony effect with more silver, if so, is there an upper limit before the amount of silver is a detriment (cost and compatibility aside)?
I added sugar at the suggestion of one of my engineering friends who had amazing results upon the addition of sugar when their batch wasn't striking. When I tried it, the batch went from a light almost coke bottle tint blue to dark with lots of striations. Once I saw this, I stuck with it. Should I cut down on, or entirely remove, the sugar? If the key thing is reduction, what would make up the difference?
I'm actually trying to prevent black, not cause it. The image file I've included of a simple bird on the punty shows the color the best that I've been able to make it. I would be very happy if this could be repeated. So far my remedy for a pot that is black has been to throw in a few grams of each ingredient into the pot and mix it with a punty.
I have the Weyl book. It's incredibly dense but I'm slowly making my way through it. I haven't heard of the other books but I'll look into them. Today, I spent a good few hours at the Rakow Library with a bibliography referencing books that mention calcedony.
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Old 12-05-2018, 07:15 PM
Dan Vanantwerp Dan Vanantwerp is offline
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Hi Bradley...I dig your bird.
I've tried making the chalcedony with straight cullet and didn't do very well. Now I batch it or use fritted cullet, as Pete suggests. Takes a little effort but just drip 10 lbs worth of molten glass into a 5 gallon bucket. Don't just drop big blobs (as if you are emptying the furnace) as this defeats the purpose. Let the glass form a <1" diameter thread as it passes into the water. You can go at the cold frit with a hammer to get it even more fine. Wear goggles!
Add your ingredients, mix very well and add much less black tin...like 1/10th. I add 3g and sometimes wish I'd added less. I think the black you see may actually just be the dark amber color that likes to form with too much black tin. Also, in order to better homogenize the colorants mix them together first. Get a pickle jar, add each powder to it and shake like crazy. If your silver nitrate is chunky, smash it with a mort and pestle (available at Target believe it or not). Add the mix to a slightly damp fritted cullet. In the proper mixture, the color should be more "iron red" than "black tin".
To make it completely error-proof make the cobalt version instead (same mix plus 4-5g cobalt oxide and 4-5g red copper). This blue version seems more resistant to blackening with even twice as much tin (5-6g). Even it it doesn't go colloidal at least you've got blue
Get away from just throwing stuff on top and mixing it in with the punty. It's tempting sometimes but definitely not repeatable. Have fun and good luck!
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