Friday, July 13, 2012

The Many Uses of Casting Investment

by Janet Alexander
Technical Advisor

Casting investment is a ceramic mixture used in the process of lost wax casting for jewelry making. It is formulated to keep its strength and integrity in high heat. It is a mixture of silicone, plaster, and other materials. It sets up in 9-10 minutes and is ready for the kiln in 30minutes.

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.

I also like to use the investment as a support while firing a domed metal clay item. I make a mold, out of modeling clay, of the dome I used to dome my metal clay. I pour the investment mixture into the mold, allow it to dry, and then use it as a support system in the kiln. This keeps my metal clay from losing its shape while firing. Since it is an open support, as the metal clay shrinks it shrinks over the domed shape. You can make different support structures for all your creative needs using this process! 

Investment dome on left with original dome on right.
As always, I hope you all enjoyed or learned some tips from this posting. Send me some suggestions for future posts and have fun claying around.

*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!


Anonymous said...

Nice one Janet.....I love the different uses you've tried cos I haven't used it since I stopped casting!

Anonymous said...

Hi. I know this is an old post but I just found it. I tried using silica free investment (from cool tools) with fastfire bronze clay. They were fired in coconut carbon at 1525 deg F for 1 hour. After firing was complete there was a sulpher smell to the kiln and the piece was black where it was touching or near the investment. Was there a chemical reaction with the fastfire bronze? Any idea what happened?