CT 8- Casting and Moldmaking

(right) Professor Bill Hole, College of the Redwoods, explains how to separate flexible molds from models. 

This spring College of the redwoods HPRT students are leaning and studying the aspects of plaster work and replication and creation of models and molds. Students learn  how to make clay models, make mother molds of plaster, latex 74, Polyurethanes, and resins in order to cast models. Advanced techniques include using oxides to add pigments to plaster to gain color attributes and mimic marble patterns, as well as, making an "horse and slipper" in which a wooden hand tool is fitted with a profile knife made of tin and fastened to wood stock with the same profile negative cut into it using a band-saw.

A running mold designed to  do mold a radial ceiling medallions (as seen below)

 Here students learn the basics of model and molds and how the shape of the model will indicate how easy it will be to remove the model from the mold. The extraction of the model form the mold depends heavily on what type of mold release is used and  what is also referred to as "undercuts". Mold releases help prevent the casting agent from sticking to the interior of the mold. Mold release can be anything from shellac, potters soap, universal mold release, vasoline, and a few other commonly obtainable products. Undercuts are where the shape of the model has a negative profile or recesses on its surface which can create a area of contact that will not allow the mold to separate from the model

Students Jordan, Chris, Elliot, and Paul pouring up a three part split mold held together by rubber bands to keep its form

Iron oxides were used to color  this garland  as an experiment in color pigmentation of plaster, as well as the decorative tile shown beloew

Rubber Mold Compound used for making a very rigid mother mold that will produce numerous castings withous loss of details. (above is the two part mix with an abalone shell as the model)