Sept Oct 2006.pub - Blacksmiths' Guild of the Potomac

again using the guide pins for alignment. Steelplates were placed on the outside to support theexposed sand, and C-clamps used to hold everythingin pace. Too much pressure with theclamps can distort the mold, so if possible theyshould be positioned to press on the edges ofthe frame rather than the center of the mold.With the mold completed and sitting upright,it was time to prepare the silver. Markuses a carbon crucible, although there are alsoceramic and plaster ones available. He estimatedthe amount of silver needed for thebuckle (this can be done by weight or by volume,tho he did it by the seat of the pants). Extrametal must be added to create the sprue, andMark measured that by simply using the silver inthe old sprue that was cut off from his last casting.Mark cautioned that not having enoughmetal will ruin your project so it’s better to besafe and add extra. Boric acid was added as aflux, and the crucible was placed in the coal forgewith a lid to keep ash out of the melt. He heatedthe metal until it was completely melted but justbelow the boiling point. When the metal reachedthe proper temperature(swirling andwhite hot), itwas stirred witha graphite rod toremove impuritiesand quicklybut carefullypoured into thespout on themold frame.After the silver had cooled a bit, Mark removedthe clamps and separated the frame sectionsto free the silver casting. Finishing wasn’tdone in the shop, but involves cutting off andfiling the sprue as well as any flashing where thesilver spread between the mold sections. Allscrap metal is saved for future melts, and filingscan hoarded and sent off for refining. A finalbuffing and soldering on any mechanical parts(like a pin for the buckle), and the piece is done.September/October 2006 7