How to make a glass blow mold from paper model.

Step 1:

Begin with a paper shape. Fill the paper shape with microcrystalline wax. Build a gate for the paper shape with wax sheets. Coat the exterior of the shape with wax.

Step 2:

Fix the gate (spru) of the shape to the table. Build a box around your shape with coddles and clamps. Leave at least 1" around your shape. Using soft clay, seal all the places plaster could leak out of the box. Your mold will be made out of plaster silica with a refractory jacket. Using the ratio of 1 lb water to 1.5 lb plaster/silica, mix enough plaster to fill the mold (always adding dry mixture to water). I use moulding plater and "silcosil" silica. Once mold is set up, rebuild the coddles to leave another 1" around the perimeter and pour refractory material like Mizzou or KS-4 as a jacket layer (for strength). Let the mold set up and then flip over. Steam out the wax.