Of Keys and Sprues in Molds

Making a mold with clay, ceramic, rubber or polyurethanes seems quite simple. All you have to do is capture the shape of the model you wish to replicate with the mold making material of your choice.

However, a lot of finer points also enter the picture. I too realized the technicalities involved only when I actually got down to the task of making a mold. I was trying to reproduce a beautiful statuette and this opened the door to learning how to make a two-part mold!

That was not all. While making the first part of the mold, it dawned on me that I should be able to join the two parts of polyurethane molds together too. I started reading up about mold keys and carefully watched a demo video before using acorn nuts for the task. I carefully placed them all along the perimeter of the first mold part. I now knew that once the other part was done, the protrusions and indentations would help me to properly patch up both the parts in the right place.

As I was getting ready to make the cast, an experienced artist happened to point out that air could easily get trapped inside my closed mold creating unsightly gaps in the finished cast. I was flabbergasted once again until he explained to be that I should make small sprue holes along the surface of the mold to allow the air to escape.

I was finally able to make a decent reproduction of the statuette and I know it’s no cut-and-dried job at all!


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