Sunday, March 4, 2012

pouring a silver ingot

pouring an ingot with my silver scraps is not as easy as it looks in the books!
there are several ways you can go about recycling your leftover precious metal and i've chosen to use an "ingot mold" because of the various sizes possible of both wire and ingots in the one mold. a friend of mine carves out ingot shapes in a charcoal block and melts the metal right there in the divot, but i've noticed that he ends up with oval shapes more often than not because the rectangle shape is too big for the amount of metal, which leaves lots of extra metal that just ends up in the scrap container again. i've heard from very knowledgeable metal smiths that using delft clay as a mold works well for pouring an ingot, and perhaps i'll try that someday too.
i will say that when i was first learning to pour the molten metal into this mold, i must have made every mistake possible. but that is the best way to learn, really! i started with some basic info from jaime pelissier's chapter on alloying (mainly about alloying gold, but it goes into troubleshooting your pour too) in the book Penland Book of Jewelry and i picked up some useful tips from the metalsmith unit 2.0 facebook group which eventually led to success.

i'm heating my NEW crucible and sprinkling it with boric powder to maintain a barrier between the crucible with its impurities and the metal i'm going to heat. this is my second crucible--i poured too much boric on the first one, way too much!

this is what your crucible will look like after you melt the boric powder in it and coat the surface

here is the ingot mold and the crucible filled with scrap sterling (no solder allowed on these scraps). this mold must be heated to remove any condensation or you will have molten metal exploding in your face as it hits the moisture.

i'm heating the metal with a nice big flame--i use acetylene

the metal is just about ready to pour--it looks like mercury rolling around in the crucible
several times that very first day, my son was sure i would set the house on fire or cause an explosion. you have to use a huge flame to melt the metal (i'm using acetylene) and you have to heat the mold to remove condensation, which will cause it to smoke that first time. this is an important step, because any moisture in the mold will turn to steam when the molten metal hits it causing it to sort of explode back at you.  to reassure him, i called the rio grande technical support hotline, and received confirmation that the smoke was normal, and continued to proceed. sadly, the pour was unsuccessful because not much of the molten metal made it into the mold. the second attempt saw most of the metal make it into the mold, so my son xavier rolled that into an 18 gauge strip, but it wasn't long enough for the money clip he was making. more attempts at getting all of the metal into the mold for a new ingot ensued, and eventually, after about 3 tries, he had something to work with. but the strip cracked after about 8 passes through the mill-- a good way for him to learn about how much stress the metal can take before it must be annealed.
remelting this cracked ingot resulted in a pinhead sized amount of metal making it into the mold--even with the nickels that i used to slant the mold to the side so air would not get trapped. well, i knew after that, that most likely i had gone through all of the possible things to do wrong, and what kind of a pour could possibly come next? yes, one where all of the metal made it into the mold, a successful pour! but where is xavier? uh oh, the wind is up, his surfboard is missing and so is his car...

just before i pour, when the metal is molten, i add some matt's casting flux to bring the impurities in the metal to the surface

i'm pouring...

hmmm...this is not where the silver was supposed to go!

but enough of the metal went into the mold to roll some sheet

this is what the ingot looks like after a few passes through the mill

xavier mills the metal

it looks great, but it isn't long enough...

this is what a successful pour looks like!

the ingot is ready for xavier to file and roll, but he's gone surfing!