I just bought a used electric furnace to make silver bars with scrap silver. I used a graphite crucible and a graphite mold. I heated to 2000 degrees F and hit the mold with a propane torch a little bit. The pictures of the finished silver bars are after sanding down to make them look nicer.
I have a question for those with experience pouring silver bars... How do you get the silver to pour consistently into the mold so it will look nice? I dont think my silver or the mold was hot enough because it was hardening as I was pouring it.
Definitely a cold pour. So, some questions pointing to things to look at: 1) How are you measuring temperature? The melt temperature measurement should be as close to a uniform throughout the melt as possible. 2) Silver melting temp is about 1760F. If the raw silver has an alloying agent it is most likely copper. That temperature is a touch less than 2000F. If there is copper in your melt and you haven't raised the temperature above 2000F and held it long enough to thoroughly melt the copper, then you will have a cold pour. 3) You have to hold the melt at your desired final temperature for a little while to allow any contaminants and alloying elements to separate. Some of those will sink and some will rise. Those that rise should be skimmed off. I use a SS skimmer for that. But don't hold at temperature for too long because oxidation is dramatically increased at higher and melt temperatures. It's a bit of an art. I developed my methods using aluminum to cast parts for my various projects. I learned much of the basics from an old Yahoo Group on the subject. Today, I am sure YouTube has superseded that venue so you should be able to get a lot of tips. Be careful. Wear good eye and face protection. I set fire to myself and almost lost an eye when a gob of molten aluminum shot out of the melt and hit my shoulder. If I hadn't dodged, it would have hit me in the face.
@desertgem yes I sprinkled some borax I just put in the set temperature on the furnace and it slowly heats to that temperature. I was definitely getting some oxidation since my pours were black/grey on most of the surface. I think I poured the silver too early. I will try again by heating the metal to 2000 F and letting it sit for 10 mins. Also heating the mold with a torch more. I was getting some rough metal on the top of the molten silver when it was in the furnace but next time I'll take that off instead of trying to mix.
From my ceramics courses I taught for a couple of years and was in charge of the Kilns . We just used clay. no metals, but both have to have constant temperature over a time long enough so the internal metal ( or clay) is equal temperature before we start to time it. Even though we had a single high level thermometer ( 2500), we used "ceramic cones" on each level so we could tell if the temperature was even and constant all around. When the peak of the cone started to bend down, we would be at temperature, and maintain it. When the tip curled down and touched the plate, it meant the temperature was correc at all levelst. Depending on the thickness of the walls of the piece we would time it and when done, turn off the heat ans let it set all night to cool down slowly. Cones are on Amazon. If I ever sub for the class from now on, I will use an infrared sensor gun, much easier! ( also on amazon) I mention this as it was possible that the heat was not totally dispersed evenly. Jim
Just a safety side note... "long" gloves or suede sleeves (better both) and apron!!! are just as important as those safety goggles... I wore mine "most" of the time and my arms still look like this (plenty on legs and chest too, was lucky to never get hit in the face...) Oh and yes a cold pour... you need to hold temp a bit longer to melt that copper but that's all been said already
