Melt Dishes and Crucible Sweating Mysterious Liquid when heated.

[Geber]

Has anyone observed liquid sweating out of their melt dishes? I have been having this problem and it makes pouring the metal impossible.

Not too long ago I bought some melt dishes, heated one to drive away moisture, glazed it, and melted some fine silver in it with no problems.

Then I used it about a week later and a liquid started coming out of the ceramic when the silver was nearing its melting point. This liquid took a glass-like appearance when cooled, and exploded with a pop when it was quenched. I reasoned it was excess borax, that the dishes somehow came glazed with borax, and that I should not glaze the next one. I then used an unglazed one, and the metal did not stick inside, but the same liquid appeared. It also seems to be taking too long to melt the silver with MAP gas and that I have to use way too much gas.

Finally, I used my graphite crucible in my little furnace. The crucible had also been sitting around in my shop, which can get damp, and I did not condition it. When it got to temperature, I looked in the crucible and saw an orange liquid. It was slightly steaming, convecting vigorously, and spitting out the occasional tiny orange spark. Thinking it was the silver, I poured it into my mold, and poured a bar which was dark-red and blackish in color. I emptied the mold and the "bar" fragmented into pieces. The silver was adhering to the side of the crucible, and was never totally melted. I did not put anything in this crucible besides silver and a little pinch of borax.

Can anyone tell me what I'm doing wrong? Do I have to drive the moisture out of melt dishes and crucibles every time I use them, and is this liquid a saturated water-borax mixture? Thanks!

 

[kurtak]

The problem is NOT with the crucibles &/or melting dish's

The problem IS that you are NOT getting all the chem washed out of your precipitated metals &/or that you are having base metal oxides, hydroxides etc. (metal salts not washed out) co-depositing with your precipitated PMs

Kurt

 

[Shark]

Does it look like this?

 

[Geber]

Does it look like this?

View attachment 65760

Somewhat

 

[Geber]

The problem is NOT with the crucibles &/or melting dish's

The problem IS that you are NOT getting all the chem washed out of your precipitated metals &/or that you are having base metal oxides, hydroxides etc. (metal salts not washed out) co-depositing with your precipitated PMs

Kurt

Thank you. I will do a better job at washing them next time. How necessary is it to heat a melt dish to drive away moisture after the first time? Do they reabsorb moisture?

 

[Shark]

Somewhat

Then Kurts reply is right on the money. That dish was brand new when I melted my first ever run of silver. And I realized to late I forgot to wash it before melting.

 

[goldshark]

Thank you. I will do a better job at washing them next time. How necessary is it to heat a melt dish to drive away moisture after the first time? Do they reabsorb moisture?

A properly sealed melt dish, will not absorb moisture on the up ( parabolic) side. The bottom could, depending on clay type used in its manufacture. So could go either way. You did not state the composition of the melt dish, and there are a variety of recipes.

 

[GuyGuyGuythe1st]

I manufacture ceramic alumina melt dishes. Just my observations. You said you using fine silver. Assume it’s not 99.9% silver, if it tiny amounts of copper in the alloy. You can get that copper/bronze stain. The green is oxidation of the copper via water most likely. You can see it slightly see green like the Statue of Liberty.

Also depend on the flux it oxides different base metals which causes a discoloration depend on other elements present.

Also unless it’s a porcelain melt dish with an extremely fine surface finish. All melt dishes are 1.) porous 2.) absorbs water based on its environment. I have to do mine every time I melt because I work in a garage that’s not climate controlled.

It’s standard practice to glaze your dishes because of their porosity and to heat the dish slowly with a torch to drive out moisture.

If you don’t do this depend on how much water is absorbed. If you immediately start to torch. You cause a steam explosion. It will crack it in half, most cases. Oxy/Acte torch will cause ceramic shards to explode. It’s not really pleasant being hit buy extremely hot ceramics.

Take my word for it.

Glazing doesn’t 100% eliminate porosity. Most jewelers and refinement companies save the crucible’s and process them later to recovery any precious metals that absorb into the dish. This is also know in the industry as melt loss due to porosity. If you’ve ever sold to a refiner. They will usually tell you this even if you weight your product prior to shipping or selling it.

Hopefully this helps!