Press Moulding

Last week I tried to make my own press mould for the first time, not very successfully. My plan is to create press moulds from composite thrown forms so I can build them together into large sculptures. I find it easier to hand build on a large scale with grogged clay, but it’s painful and not very effective to throw with heavily grogged clay, so I will create press moulds of the thrown objects instead. These forms will be for my final individual project . I’ve narrowed the brief down to explore the imagery of in Italo Calvino’s ‘Invisible Cities’, Ch. Thin Cities 3, especially the idea of a network of pipes as underground veins…

“Whether Armilla is like this because it is unfinished or because it has been demolished, whether the cause is some enchantment or only a whim, I do not know. The fact remains that it has no walls, no ceilings, no floors: it has nothing that makes it seem a city except the water pipes that rise vertically where the houses should be and spread out horizontally where the floors should be: a forest of pipes that end in taps, showers, spouts, overflows. “

I began by bisque firing a form I’d constructed from thrown sections then made a two piece plaster mould of this. The ceramic got stuck in the plaster when I tried to release it, either because I hadn’t used enough soft soap or because I hadn’t placed the middle line in the exact centre.

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Since for press moulding it doesn’t matter that the plaster is completely sealed together (unlike slip casting), I used glue to stick the broken plaster pieces together.

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This afternoon I’ve been making press moulded shapes ready to start sticking them together tomorrow to build large lattice structures.

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Alongside these I’ve been throwing functional ware for the anagama firing we’ll do at Naas in a couple of weeks. These 500g bowls are a little on the heavy side, I’m still a little afraid I’ll turn off too much clay and end up with a hole. I’m been experimenting with the angle and depth of the footrings to see what looks best…

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Hot melt rubber molds

I took part in my first ‘open house’ workshop today where I learnt how to use the hot melt vinyl compound Vinamold/Gelflex to make flexible moulds. Much cheaper than silicone, it can be used to cast all sorts, from plaster to wax, resins and ceramic material.However it does have some drawbacks, namely that it shrinks over time and when used with plaster or wood they have to be soaked first in water.

The Vinamold is first cut into sugar-cube sized chunks which is a bit of a challenge but is easiest done with a stanley knife and scissors. The texture is similar to that of tough meat. Next it’s heated in the microwave to around 150C which took around 6 minutes for  a full Pyrex measuring jug, a little longer for larger quantities. It’s best to check the consistency every 3 minutes or so in case it begins to burn. The objects we wanted to make moulds of were placed onto sheets of clay with a cottle to give a gap of about two fingers width in between. When the compound was of a runny, soupy consistency it was poured into the moulds and left to set for about an hour. It was easy to release the objects from inside and every tiny detail is captured. The process is so much quicker than making a plaster mould.

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