Haveing trouble with pours

[Brian]

I'll try and explain best I can what I'm doing, without dragging this out into a 3 page book.


I melt down scrap that has only carbon/ tungsten and silver in it. I made my first furnace based on the stuff I bought on line. What I had bought was the hand held crucibles with the tongs and some borax. So I built a furnace based on the blast furnace for working steel. It sets sideways with a hole in the side. I put my crucible in and do melts with mappgas that the flame directly hits the sliver, melts I pour it and carbon and tungsten go to the top of the pour. I file it off and melt again until none remains, usually takes 3 times. I've done this for the last 6 months. Well my furnace is disintegrating and starting to fall into my pours, it's a paint can, filled with plaster Paris/sand mixture. So today I got out a new crucible, did the borax glaze and did melts in the open air..... It melted fine, but the pours look like crap. Just trying to figure out why? And I think I need a whole new set up. I do a ton of melting, but bulk doesn't equal knowledge. I'm a noob at best.


First picture is crap I poured today

Second are pours I did before.

 

[Brian]

Just wanted to add, in the furnace the crucible stays glowing from the heat, open air, it stays white.

 

[FrugalRefiner]

Molten silver can absorb something like 9 times its volume of oxygen. When the silver cools, the oxygen has to escape. In your furnace, you probably have a reducing atmosphere (i.e., an atmosphere low in oxygen) because the available oxygen is being consumed in the combustion of the MAPP gas. In the open air, you'll have an oxidizing atmosphere which has plenty of excess oxygen that is available for the silver to absorb.

Dave

 

[Brian]

That makes sense.... Thanks