The yellow mapp right? what head is on it? Best way to treat a crucible is put a hand full of borax in there, melt it and turn it sideways letting all the hot borax drip out. :lol:
Yep yellow, I borrowed a head from a friend doesn't have anything on it. Does that make a difference?
Does anyone know where i can get one of these? http://www.ebay.com.au/itm/TONG-MEL...CRUCIBLE-DISH-HOLDER-WHIP-LARGE-/200529047540
http://www.gemcuts.com.au/whip-tong-with-ceramic-melting-dish This is ont that holds 60mm dish for small pours not sure if they have larger ones
Thanks guys, was hoping to get it before the weekend but probably not. Can i save my crucible? I have tried everything but cant get it clean. Should i get some sandpaper action happening?
The sides with the silver/borax bubbles...After cooling down the borax in the crucible can be heard cracking is that normal? Also do i need a oxy torch as the mapp one doesnt seem very hot, take a second or 2 away from the silver and it starts to harden up again.
Correct on both counts Correct, it looks fine I can melt 10-20 Oz of silver easily with just a propane blowtorch. BUT - in a graphite crucible, and in a furnace. Oxy-Acetylene is great for gold in a fused silica crucible like yours, but for me, silver tends to fume (silver vapor going up in smoke I believe) It's probably just my welding tip, too hot in a small spot, as others do use a big oxy on silver with no issues. (as I understand it, although silver's boiling point is about double it's melting point, it has a low vapor pressure, which can cause it to fume away at temps well below the boiling point) So I think your main problem is not the torch temperature, but with keeping the heat in the crucible. Are you placing it on something that doesn't conduct the heat away quickly? Maybe you need to make some type of a furnace (using perlite mixed with refractory cement or sodium silicate). This will insulate the crucible, and keep the flame's heat enclosed around the workpiece. Because melting in graphite always seems to result in some scum on the poured bars for me, I'm going to try making such a furnace for a fused silica crucible, and some tongs to suit. I expect very shiny pours from that, with just a small amount of borax to keep it clean. Borax can be cracked off when there's as much as in your photo. Smaller amounts will dissolve in dilute sulphuric acid, maybe with some heat.
Thank you for the explanation! I had to put the crucible on a concrete floor maybe that is acting as a heat sink. I will be ordering tongs soon so that should help with the pour i hope, using tweezers is too fiddly!
I'm not sure if anyone is keen and able to refine but I have a large silver bar that was approx 65% from a xrf reading of both sides I have an iPhone 5 case next to it to show size. IF there is any interest in buying it to refine I'm happy to sell at spot and can weigh it and quote a price. I think it was around 700g or so
Here is another photo. I think I worked it out to be about 14oz of pure silver at 65% silver As I said, happy to let it go for spot
Finally got around to using the new crucible holder and it makes a big difference to the pours. Did a half decent job. But need to find out how to remove the remaining borax? Also how do i deal with the pin holes in the silver? Best one out of the bunch.
one way you can get the borax off is to have white vinegar in a small pot and get it to boil with the bars inside - wont take long to dissolve but it smells out the kitchen - as for the pits, its hard to avoid them when you are using borax as that is were the borax was nice job on the pars by the way
Looking much better! Very clean silver. What was your source material? I don't know what causes the pin holes, could it be still needing a little more heat? Let the melt get good and hot before pouring, the surface tension should draw it into a button, with no part of the melt still trying to stick to the crucible. Also, are you heating the mold before pouring, to help stop the metal cooling too quickly? Meanwhile, back at the ranch... Getting better at this myself. 2 and 5 ounce bars, finally with no scum. Using a fused silica crucible with borax. (some borax spots on the 5oz's) And a couple more 5 oz bars. The one on the left is exactly as it came from the mold (except for the water quench) There's a couple of borax spots on it. The one on the right was heated in dilute H2SO4 to remove the borax.
