Hot-Blow-Molds (small/vessel)



By pre-heating plaster/silica molds in a kiln before blowing into them, you can achieve a level of detail that is comparable to casting, but that gives you more control, as is with “hot-work”. Once annealed and coldworked, the glass can be picked back up hot and further manipulated.





General Technique

Forming and shaping

Specific Technique

Mold-making/ Glass-blowing/ Hot- Assembly

Properties & Qualities


Art Sculpture Product


Pink Brown Red Yellow Other

Sample Information

Date of creation

Feb, 2021

Process & Production

Similar to the lost-wax casting technique, these blow molds begin with a wax positive that will be invested in refractory material (plaster/silica) and steamed out, leaving a negative space within the mold. 

When the mold has dried, it can be placed in a kiln and brought, slowly, up to 550 Celsius. Once up to temperature, the mold can be blown into – annealing the mold and the glass together. After annealing, the mold can be broken open and the glass cold-worked. 

Because this is a small-scale vessel – no stuff cup is needed. However, it will be an open vessel and I want different colours on the inside and outside. Therefore a double overlay (using solid bar-colour) is necessary.

After breaking open the molds and carefully coldworking the glass, it can be placed in an oven and brought slowly up to temperature to be picked back up and assembled hot in the hotshop, simultaneously fire polishing any cut edges.

Recipe Details

Mold-mix: 50/50 plaster/silica, reinforced with woven fibre glass on the 3rd and 4th layers.

Colour application: layering multiple glass colours while hot by rolling fresh gathers into glass powders


Craft Maker

Sadhbh Mowlds

Library Contributor

National College of Art & Design Ireland


Sadhbh Mowlds