Plaster press molds are very useful when you are planning to make multiples of a particular form or an embellishment to a form. For Allistair and Sally MacDonnell, press molds really came in handy for a series of ceramic brooches that they wanted to make.

 

In today’s post, the MacDonnell’s show us how easy it is to make plaster press molds. Plus they explain how they use stamps to texture each slab before molding it into the shape they want. – Jennifer Harnetty, editor.

 


 

This article was excerpted from Ceramic Jewelry, which is availablein the Ceramic Arts Daily Bookstore.



Fig.1 Modelling the nose onto an egg form.

Fig.1 Modeling the nose onto an egg form.

Fig.2 Modelling the lips.

Fig.2 Modeling the lips.

Fig.3 Creating the chin.

Fig.3 Creating the chin.

 

Plaster of Paris Molds for Handbuilding

 

Molds are very useful to speed up the process of repeating forms. Plaster is cheap and can be bought from specialist suppliers in a dry state. As shown in the illustrations, the Macdonells make plaster molds for their brooches. Here the modeled face is attached to a slab of clay and surrounded by a cottle (clay wall). The plaster of Paris is then mixed as follows. Firstly, the volume of plaster needed is estimated by looking into the cavity created by the cottle (the surrounding clay wall) and estimating the amount of water needed to fill this space. Now half the estimated amount of water (the amount of water actually used is only half because the plaster expands in the water to fill the space within the cottle).

 

Fig.4 Modelling the eyes.

Fig.4 Modeling the eyes.

Fig.5 The modelled face is placed onto a clay

Fig.5 The modeled face is placed onto a clay slab.

Fig.6 A clay wall surrounds the face.

Fig.6 A clay wall surrounds the face.

 

Pour the final amount of water into a large bowl or bucket. The plaster is then sieved over the surface of the water until an island of plaster appears, whereupon one more handful of plaster is sprinkled around the outer edge of the water in the bucket. Leave the plaster and water for a couple of minutes until all the plaster has been soaked through, then gently agitate the mixture from the bottom until it becomes thicker, being careful not to introduce air into the mix. When the mixture begins to thicken, it can be poured into the prepared cavity. It is then gently pushed down to ensure that the plaster has been forced into every detail of the model and that air bubbles have been encouraged to the surface. If the estimated amount of plaster is not enough, then the surface should be roughened by dragging a finger through it as it is becoming solid, so that another mix can be made and poured over it. If too much plaster has been mixed then the excess should be poured into a rubbish bag, NOT down the sink, where it will block the drain hole.

 

Fig.7 Plaster of Paris is poured into the cavity.

Fig.7 Plaster is poured into the cavity.

Fig.8 Handmade bisque-fired clay and plaster stamps for making impressions.

Fig.8 Handmade bisque-fired clay and plaster stamps for making impressions.

Fig.9 Textured clay ready to be pressed into the

Fig.9 Textured clay ready to be pressed into the mold of a face.

Fig.10 The press-moulded face with impressed

Fig.10 The press-molded face with impressed patterns still showing.

Sally and Alisdair MacDonell, Face Brooches, 2008. Nine awaiting glaze application and nine fired, finished with cobalt or copper oxide and a matt white stoneware glaze, 30 x 40 mm (11?4 x 11?2 in.). Photo: Dan Bosworth.

Sally and Alisdair MacDonell, Face Brooches, 2008. Nine awaiting glaze application and nine fired, finished with cobalt or copper oxide and a matt white stoneware glaze, 30 x 40 mm (11?4 x 11?2 in.). Photo: Dan Bosworth.

Click here to leave a comment