In the metal clay community it is used as a place holder to keep the metal clay from shrinking too much in certain places.
One well known use is making small patties for fitting inside rings. These patties are inserted into metal clay ring and then fired with the ring. These inserts are made by mixing cool water with investment and then pouring the investment into a ring mold. The mixture should be thick like pancake batter. After the investment sets-up, the plugs are easily removed by flexing the rubber mold like you would an ice tray. I make several plugs of each ring size and then store each size in separate plastic bags. This way I have plenty ready for my classes. After firing, remove the plug from the fired ring (after the ring has cooled) by pressing the plug outward with a spoon or carving it into small pieces using a dull knife. Dump the used investment into the trash.*
Another use for investment is as a place-holder for a stone. If you are setting a stone into your metal clay piece after firing, then place a replica of the stone made from investment into the setting. You can easily make a mold of the stone by using modeling clay.
Roll the clay into a ball and flatten it so that it is wide and tall enough to hold the stone. Press your stone into the clay (face-down) until the bottom of the stone is even with the top of the modeling clay. Remove the stone and pour in your mixture of investment and water. After the investment sets, remove it from the mold. The modeling clay mold material is reusable, so wash the investment dust off and save it for another time. Before firing your metal clay, place the investment stone into your setting.
|Investment dome on left with original dome on right.|
*Never pour investment down a drain. It settles in the pipes eventually clogging the pipes. Its best to pour any leftover mixture into a trash can and then wipe your mixing bowl clean with a paper towel. Always keep utensils used for mixing chemicals separate from food use!