An attempt to inject wax by hand

Someday I want to be able to cast precious metals like gold and silver as well as other metals with great detail maybe in Pewter or other white metal. A common thing to do in this process is to make a flexible mold either out of rubber or RTV. This mold is then injected with wax to create a master for use in lost wax casting. (An example of this type of mold can be seen elsewhere on this site under the RTV molds in that section of the book). You will find many jewelers that will do this. They have either created the piece themselves or have ordered the mold from somewhere. The procedure usually uses a piece of equipment specifically designed to inject wax. The costs vary depending on what the machine will do. I have seen them cost anywhere from $300 and up. Being on a feeble hobby budget, I decided to try to inject wax by hand to see if it could be done.

Like any other NET-AHOLIC, I searched to see if anyone else before me has tried it and what their success was. My search turned up the following page: (Looks like it may be gone now)

The gist of the article was to clamp your mold in between two aluminum plates, heat the wax and use a syringe to inject it into the mold. My experiment follows:

Needed materials · · · MATERIALS
  • Old Candle
  • Old Pot
  • Syringe
  • Small Glass Container
  • Petroleum Jelly
  • "C" Clamp
  • Mold

TEST #1:

Procedure: I placed the pot on the stove with some water in it. Next I took the candle and put it in the glass and placed it in the pot of water and turned the burner on. While the wax was melting I lubricated the plunger of the syringe with some petroleum jelly and clamped my mold together with the "C" clamp. When the wax had fully melted I pulled the syringe full and injected it into the mold.

Result: The mold seemed to mostly fill with only a few places of trapped air. (These could have been caused by a cold mold.) Otherwise the wax seemed to catch a lot of detail. Next I tried to remove the wax model from the mold. Unfortunately the wax broke before I could get the piece extracted.

Conclusion: I would not have called the attempt a complete failure. I was able to inject the wax by hand and get most of the detail. Things working against me were:

  1. Candle wax may not be the best wax to inject with as it seems brittle on its own.
  2. The mold I used was originally created to cast pewter. The RTV was fairly stiff and gripped the wax model tightly. Additionally, there were vents cut into the mold that would not allow me to keep pressure on the wax until it solidified.

TEST #2:

Procedure: I decided to try it again with a different mold. Otherwise it was the same procedure as above in test 1. The mold used in this attempt was a mold I made for the Trollhalla coin. The coin is the diameter of a silver dollar and a little thicker.

Result: The mold seemed to mostly fill and capture most of the detail. The only real defects were shrink cavities. I was able to remove the model from the mold without breaking it.

Conclusion: The mold I used this time only had one riser. As a result I was still not able to maintain pressure on the wax. Without the ability to maintain pressure on the wax, it is free to shrink as it solidifies. One reason I think is because there is not enough wax in the sprue to feed the casting to prevent it. I am going on the presumption that wax cools like metal.

Final Thoughts: In order for hand injecting to work, I believe that it is important that you use a mold with only one opening to inject wax into with no external vents. The molds that I have created up to this point are all designed for gravity casting lead or pewter into and as a result have vents and risers cut into the mold. I also think that it is important to keep a steady pressure on the wax as your injecting it from the syringe. The reason is to help prevent shrink cavities. Another thing I would think useful would be to heat the syringe with the water your using to melt the wax to help slow down the cooling effect of the cold syringe. Whether or not that is possible with the plastic syringes I have is unknown and untested by me. I am pretty much set on making my own wax injector and not trying anymore hand injection, I do however have one RTV mold that has not yet been cut with sprue or vents or risers. I may try one more time just to see if it works. If I get around to it I will post it as a follow up to this article.