Mold making - My first mold part 3

Back to part 1
Continued from part 2

I removed the foil and found myself faced with this.

Its a solid blob of set plaster. I looked at it a lot.

There is a slight seam so the plan was to put a knife to the seam and twist, but the plaster its still wet enough that the knife just cuts it. I think it needs to be bone dry and brittle.

From what I've read the drying times vary with the amount of water used in the mix, but more on that later.

I wait.

In a pleasantly surprising sort of way, 24 hours later, the mold came apart.

The plaster had run down the side of the botom mold and stuck to it where there had been no soap. All I had to do was apply enough force with the twisting knife to break the rim that had stuck and it came free.

I need more soap next time. Or rather I need some soap down the sides a bit next time.

Even more pleasant surprise, as the model also released cleanly.

There are a lot of bubbles in the plaster, but I'm reading of some ways to combat that. More on bubbles in a future post.

The roughness visible in the half on the left is a faithful reproduction of the actual roughness of the original.



To round out the trilogy of pleasant surprises, it also turns out that the lumpy bits that were on bottom mold, and their reflection in the top mold serve a very useful purpose. When you replace the two halves, the lumpy irregularities make it easy to align the parts perfectly. Lumpy irregularities turn out to be called "keys" in the mold making world. Keys are often added to aid in aligning the pieces of a mold.

Bubbles aside, the mold looks pretty good. It's quite an interesting thing to crack the mold and remove the original model. It's not often we get to see the negative of a 3D shape. Especially one we make ourselves. The plaster does an amazing job of faithfully reproducing every detail of the original.

Back to part 1

Back to part 2

WARNING !!! Plaster can get very hot when setting 

google search for: plaster of paris third degree burns