Casting

Hi,
I am reprinting the last part of my previous blog post here and adding to the discussion.



I also decided that I would do a multi part blog post on the lost wax casting method. Here is a sprue tree of wax that is going to be cast into silver soon.

This sprue tree will be put into a flask and the flask will be filled with a plaster like substance called investment. Lots of work gets done along the way to help produce clean castings (surfactant wash, debubbling investment, deseaming wax). Once the wax has been encased in the investment, the flask is allowed to dry for a few hours.

Then, the flask with the wax encased is put into a high temperature oven. For me, and everyone does this a bit different, I burn out the wax over about 12 hour time frame. The first stage of burn out is to drive off all the excess water. The next stage melts out almost all the wax leaving a negative space, hence the name lost wax The next stage is a slow ramp up to 1350. This turns what little stuff is left over from the organic material of the positive copy into gas and clears out any and all left over wax.

The flask is then ready for casting. I use a vacuumed method for casting, many other folks use a centrifugal method. I could not tell you which is better because I learned on vacuum. The flask is placed into a special vacuum chamber and the molten metal is poured into the negative space.

The result is a silver copy of the sprue tree you see above. Then the fun begins :) Actually the whole thing is extremely fun. For those of you that have tried home black and white dark rooms, the experience is like watching your image show up in the developer, but a whole lot longer and a whole lot more exciting.



Here is the cast sprue. You are seeing raw sterling silver. What you are seeing is exactly what the metal looks like after all the investment has been removed from the metal. This clean up step takes me about 30 minutes to remove all the investment. It is important to remove it all because the investment is made up of microcrystaline quartz. Microcrystiline quarts is not good for your lungs. Some folks have expensive equipment to high pressure wash off the investment. I use a tooth brush, some dental tools and my ultrasound cleaner. The ultra sound is a life safer on time and effort for this task.