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Old 07-05-2021, 02:06 PM
Bradley Howes Bradley Howes is offline
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Oxidizers and reducers

Hello All,

I figured Iíd put this thread in here rather than the color section just cause itís a small question. Iíve been tossing around the idea of batching a base calcedony glass and adding a spectrum of oxidizers and reducers. My thinking is to make a spectrum of glasses that range from extremely over reduced to completely oxidized.
Iím thinking about using sugar for reduction. As for an oxidizer, I canít think of any that would Ďburn awayí like sugar does. Nitrates would leave behind some extra alkali and I think I heard that arsenic and antimony donít play well with calcedony. Anybody have some thoughts or avenues I could explore?
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Old 07-05-2021, 07:13 PM
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Pete VanderLaan Pete VanderLaan is offline
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simply put, oxidizers donate oxygen to some other molecule and reducers take something away from one.

These glasses don't want more oxygen in my experience. They do want to be opacified ( zinc) . I make mine with nitrates and have yet to try chlorides since the nitrate ones work rather well, except they're a bitch to fine out. Melt cold and neutral. Stay away from sodium.
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Old 07-16-2021, 06:19 AM
Jed Hannay Jed Hannay is offline
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Quote:
Originally Posted by Bradley Howes View Post
Hello All,

I figured I’d put this thread in here rather than the color section just cause it’s a small question. I’ve been tossing around the idea of batching a base calcedony glass and adding a spectrum of oxidizers and reducers. My thinking is to make a spectrum of glasses that range from extremely over reduced to completely oxidized.
I’m thinking about using sugar for reduction. As for an oxidizer, I can’t think of any that would ‘burn away’ like sugar does. Nitrates would leave behind some extra alkali and I think I heard that arsenic and antimony don’t play well with calcedony. Anybody have some thoughts or avenues I could explore?
Sugar is sure convenient, but Powdered Graphite from general pencil (?) is a good source of clean C if that’s the route you want to go.

Using Cu or Mn for this series instead of Ag might yield easier-to-interpret data about the redox state of the finished melt, if it’s just the redox spread and redox agents you’re interested in exploring.

If you choose to use Ag remember that silver nitrate will bring additional O2.

Schmidt lists K2CO3 : KNO3 as 1:1.46 for substitution but 1:1.5 is pretty close.

Probably good to run one with no C and no KNO3 first just to see where you’re at.

Best of luck!
-Jed

Last edited by Jed Hannay; 07-16-2021 at 06:33 AM.
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Old 08-03-2021, 09:32 PM
Hugh Jenkins Hugh Jenkins is offline
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Why make this so hard. Start with a clean batch with no added oxidizers or reducers. That means leave out the nitrate and antimony in most batches. You only have to worry about the "free oxygen' not what is tied up already in silica or lime or alkalis.
The amount of nitrate in the silver is so little that it can be ignored for the most part. Tin really alters the opacity of the silver batches but both white and black tin oxide will work but in different amounts. Zinc can help in dissolving heavier metals. All batch components need to be completely, totally and thoroughly mixed.
The reducing agents can be sugar, silicon carbide grit, or graphite, but all have different impact, and should be used very sparingly. Small amounts of sulfur is very powerful.

A lot of interesting stuff can be gotten by just pouring the silver nitrate solution over the batch and only somewhat mixing it in. That inconsistent concentration throughout the melt is very significant. An even luster would require more complete mixing.

Melting silver glasses is very easy actually but the results will not cross the street. How you run your melt, the degree of reduction, how you cool down, or oxidize for any period in the melt, contamination of other metals in the batch or in the crucible, all can cause unique results. I only know melting silver in fuel furnaces. No experience in electric melting but I am certain that the chemical reducing agents have to be reconsidered.

Read the books before you ask questions.
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Old 08-04-2021, 08:28 AM
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Pete VanderLaan Pete VanderLaan is offline
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I melted them in the moly with no downside effects. I always melted pretty cold, under 2200F, then turned it up. Those glasses are really difficult to fine out and take me two heating cycles. I sometimes wonder what the addition of fluorspar might do.
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Old 08-10-2021, 06:57 PM
Jordan Kube Jordan Kube is offline
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There are many questions that have already been answered but if I have a question no one has an answer to I like to do an experiment.

Those that missed the Croucher/Peiser class at Penland missed out. I felt so fortunate to be there and to have done my homework. There is still so much to learn, even if it gets spoon fed to you. I do appreciate the spirit of openness, sharing, and curiosity that Bradly has.

Just as Hugh says, read the books. They're not wrong. They talk about a lot of stuff we don't practice. Think about things in industrial scales. If it works for industry it might work for you. That's how we got to where we are today.

As I remember it, John could correct me, or not, Gaffer uses salt cake(sodium sulphate) vs antimony. Production for yourself vs production for the world are two different things. I use plain old sodium chloride for boro melts and it would be interesting to see how that works for soft glass. For a reduction agent they use use silicon metal powder. Think about that. Tin still has a place though but silicon is cheaper if that's what you're after as a reducing agent.

Please report back.
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Old 08-11-2021, 07:14 AM
Jed Hannay Jed Hannay is offline
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With enough Na2SO4 and Si powder, you too can make one of your furnaces barf out a huge foamy mess.

Super educational moment for me personally. I don’t generally use sulfates of any sort. I don’t melt hot enough for oxidized fining with Na2SO4, and apparently lack the furnace headspace for reduced sulfate fining. That’s ok. One less source of airborne sulfur.

I’d post pictures but I’m not sure which buttons to push. Happened just a few weeks ago after “careful study and research”.

Si metal powder is an “elegant” reduction agent, though. Good stuff.
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Old 08-11-2021, 08:00 AM
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Pete VanderLaan Pete VanderLaan is offline
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I have used the saltcake but didn't get a good enough improvement on fining to keep it up. That was on silver melts. I don't use silicon metal for a simple reason: I don't want to buy chemicals at this point to add to the excessive number of them I have here. It would certainly work as a reducing agent. If I do some of these melts again, I will try adding the fluorine. One of the things in my opal silver melts is the use of potassium which does indeed increase opalescence, color tone, and luster but has the side effect of really increasing the viscosity of the glass and that makes it harder to fine out. Mark calls a lot out of the blue now but I don't hear that much from John who seems to be enjoying his retirement.
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