I am wearing the new Signet Ring so all went well. Lots of steps in the casting process.
The flask was filled with the mold material called investment. Looks a lot like plaster but it is far more complex material than plaster. This is a special investment designed to work well with 3D printed resin models.
It sets solid in about 2 hours. It then begins the kiln firing process. There is a precise series of temperature changes that are required for the model to melt and burn out and for the investment to become baked hard and a bit porous so air can be drawn through the investment by a vacuum pump.
The burnout process takes about 12 hours before the casting can begin.
The flask cools to 900 degrees and is held at that temperature for at least 2 hours before casting. The silver is poured into the hot 900 investment mold using a vacuum pump to pull out the air as the liquid silver pours into the mold space.
10 to 15 minutes after the pour. The flask, investment, and cast metal is dunked into a bucket of cold water that disintegrates the investment and frees the casting from the flask.
The silver casting is usually black because of the copper content in Sterling Silver. The casting cleaned of remaining investment. Sometime in an ultrasonic cleaner, then it is put into a hot acid bath called “pickling”
The acid removed the blackness and the surface copper and the silver casting can look snow white. That’s the color of pure silver before it is polished.
From this point on it is a series of removing the sprue and total refinement os the surface using files and all types of abrasive procedures.
Silver can be finished as bright as a mirror or have areas purposely blacked for artistic effect. The Ring has the background blackened behind the initial K.
The following pictures show the story.
|Flask freshly filled with investment. Water on top sign of good mix.||Burnout complete. Holding at 900 F Deg.|
|Casting station. Vacuum table, melt furnace.||Ring remloved from investment. Black scale|
|Uktrasonic cleaning||Ready for sprue cut-off and detailing.|
|Finished ring with dark background.|