Now, I am no expert by any means …. but I have just cast a piece that has 50 components and each of them is cast. 24 moulds all told, some of them very unsuccessful and some of them fine, especially after remaking them. So, I thought I would share a bit of experience with those who are, or maybe interested in casting stuff.
It’s a sort of CraftGeek post and probably not that interesting to most of my regular readers.
Crystal Resin … called by many different names, comes as far as I can see in two forms. One is cheap, styrene based and stinks out your house/workshop and still smells weeks after it has cured. It reminds me of boat building and car repairs (body shop) where they use cheap “fibre glass”. I did use some, it shrinks a bit as it cures…so you need to top up your moulds.
The much more expensive variety, the one I used is Gedeo Crystal Resin, is more like an epoxy stuff having two parts which you mix rather than the one above which is mostly one substance with a catalyst setting agent. Neither of the components smells much and with both you can use washing-up liquid to clean stuff (though it can set on your sink). It can be cleaned off when nearly dry with nail varnish remover. This resin shrinks slightly too. To avoid air bubbles in enclosed moulds it may work to mix the stuff up about 30 minutes before you pour, and then fill the mould in stages, allowing the bubbles to disperse a bit at a time.
Both of these tend to take a long time to dry/cure and this places a bit of a demand on your moulds. If you use plaster or resin support moulds this stuff will seep out and stick to everything … except fully-cured (24 hours at least) silicon rubber. I started out making thin silicon rubber moulds and support moulds of resin or plaster and have changed to using almost solid rubber moulds with drainage pipes of various diameters for support. The uPVC pipes are stiff but slightly flexible so that if the resin sticks to it you can ‘flex’ it off when dry.
This is the sort of thing. I split the pipe into two, lengthwise and just gaffer tape the two together…. fill with rubber and then cut out the original model.
Crystal resin takes ages to set so you can mix it early and it still pours 6 hours later, but it starts then to thicken. I use lacquer colours, (smell like nail varnish) to tint the resin, but make sure they are transparent colours. The resin will still move/bend even 48 hours later if it is a large mass, so leave it flat, not perched so it can bend under gravity.
Jesmonite resin is another user friendly resin, no smell and water cleanable if you act fast. I used a black pigment for the base of my piece and it turned out a sort of pewter grey, very attractive. It can be polished and takes paint well.
The only thing I would say is that it is a little brittle, especially if you don’t give it plenty of time to set, say 2 days. So, on the base I followed up my colour coat of resin with a layer of glass fibre then made sure I ‘wetted’ through the glass to the coat beneath…but….I did mange to leave a couple of tiny gaps which had to be repaired afterwards as they were ‘voids’ which then collapsed.
This stuff goes off in about 20 minutes so although it doesn’t seep though moulds like the crystal resin, you do have to work fairly fast and mix up smaller quantities.
I used thixotrope as a thickening agent when I was trying to get it to stick to vertical surfaces… that works fine.
I’ll be using both these substances again…. and silicone rubber for moulds … lots of it.