Impact of refining agents on colors

[Kraig Richard]

http://www.glafo.se/pdf/gt3-00_65-71_CS.pdf

[Jon Myers]

Non nitrate refining would be helpful in the color world as well I would think...

[Hugh Jenkins]

Nitrate and manganese work well together. The real point here is that you really have to know how these additives for color and refining interact. There have been snippets of this information on this board over the years. Great to see it compiled and verified by absorption spectra and fining results for so many combinations of at least the most common colorants.

Did you ever think when taking basic chemistry that knowing oxidation potentials would matter much in your life, other than to understand rust?

On the Peter/Paul tradeoff, does substituting a sulfide for a nitrate really gain anything in the exhaust emissions?

[Pete VanderLaan]

I certainly thought it would impact costs in a bad way and I have never found sulphides to be your friend in a melt.

[Dave Bross]

I was just reading about sulphur in Volf's "Chemical Approach". He said that another reason sulphur gives trouble besides the reboiling issues is that unless it is used with very coarse sand then you get fine seed that won't go away.

I do want to try that MoS2 selenium red though, so I suppose I may know more in the near future.

[Pete VanderLaan]

well the key in sulphur in reds and yellows is to recognize that cadmium by itself in a melt yields a colorless glass. Only with the introduction of sulphur do you see color. Cadmium sulphide will yield the yellow or following the addition of selenium, the red, but the proportion of sulphur to cadmium in the compound cadmium sulphide is not what you really want. Subsequently, using cadmium oxide with sulphur from other sources will usually yield much better control of the color and the blisters that the overage of sulphur presents.

[Dave Bross]

Thanks Pete.

I was way curious after seeing the other info on fining with Molybdenum Sulphide in the other "scalped pot/glafo pdf" post, and the stuff a while back in that other pdf about different reds, so yesterday I batched up a glass with the Glafo fining amount suggested, .5 to 100 ratio of MoS2 to sand, which made for .35% MoS2 and also .5% selenium. It made a beautiful amber. Very similar to the old Fenton Amberina (I think that's the one that's amber with red highlights) but not as red.I wasn't able to strike any more red into it via heating and cooling, but I was able to get it a bit redder by heavy reduction in the glory so I guess I need to head a little farther in the reducing direction to help hang on to more selenium in the melt or at least get what's staying there into the correct valance, somewhere short of "brown out" from selenide formation. I melted it neutral, no oxidisers, no reduction.

It's not much sulphur, and so far no sign of tiny seed yet, just big bubs that should be pretty easy to get rid of. We'll see what happens with temperature changes. I need to go read some more and see what the molybdenum might do in reduction too.

That's another annoying thing about selenium. It's expensive and most of it goes up in smoke in the melt.