Clay, Resin & Silicone

I've spent most of the weekend attempting to solve the problem of a former for the Georgia Jacob lamp copy - this is costing me an arm and a leg.

I started by taking a clay imprint of the the resin impression of the genuine lamp to make a positive. The main problem was that, while half of the mold was perfect, the other half was total rubbish - and it came out in two halves.

I joined the two halves with more clay and let it set, but it was still imperfect and oval, rather than circular.

I thought cutting it in half (perfect half and imperfect half) and then recreating the imperfect half by hand, again using clay, would be the best solution. 

As it happened, Hay was having a ceramics class with her sister and I hoped she'd accommodate me, but she was half way through making an ashtray (we don't smoke). 

To give the good half some stability, I thought I'd give it a thin coat of resin and, just as I'd covered it, Hay popped her head in the kitchen door and offered to try to recreate the missing half. Too late - it had to dry first, and that could take 12 hours.

Anyway, I still had a lot of clay left and, while I was waiting for the half-mold resin to harden, I tried my luck at fashioning a complete former, using a solid ball in the centre of the clay as a basis for the shape. 

Looked more like a blancmange.

As it dried, it cracked open in several places, presumably because while the clay shrank, the ball that was encased in clay didn't, leading to stresses.

Back to the half-mold. I had the thought that, even if I made the missing half, I'd need to cover it in silicone rubber to prevent the resin impregnated cloth of my copy lampshade from sticking to it. The problem here is that simply pouring the liquid silicone over the mold would probably lead to the silicone pooling due to the hydrophobic nature of the stuff. OK, it's not hydrophobic that I actually mean, but its the propensity it has to stick to itself and nothing else - it would cover parts, but run off other parts and create a lacework pattern. I'm probably very wrong about that, as the liquid tends to stick to everything like nuclear glue (mesons).

Back to square one.

I had bought some Staedler, FIMO, air-hardening clay, which is not as wet or sticky as normal modelling clay and more like plasticine, so I decided to go for broke with a revised system. 

I wrapped the base of the original lampshade in cling film, which is difficult at best, as it tends to stick to itself and refuses to mold to the concave contours of the lamp, but I finally managed it. I then took the block of FIMO clay and rolled it out like pastry to just under 1cm thick. This I laid over the upturned base of the lampshade and pushed it into the various folds and crevices, reinforcing the concave elements with additional strips of clay to hold it in place.

The little circlet of clay at the top is just to provide a base for it to stay upright when dried and turned over.

The outside dried overnight, but the lampshade was firmly lodged within the clay casing. With Hay's assistance I managed to eventually tug it free and the result was brilliant.

The inside was not yet hardened, having been protected from the air by the cling film. Next I had to translate this into a positive impression by filling it with liquid silicone. Now, the mixing ratio for liquid silicone is 100 parts silicone liquid to 3 parts catalyst, thus thorough mixing is needed to ensure the catalyst spreads evenly through the silicone liquid.

I used about 600gm of liquid silicone to fill the 'vase' I'd created to a reasonable depth, hoping the liquid wouldn't penetrate the clay and result in a claggy, mixed interface of silicone and clay.

I should have taken more time and applied a thin, sealing layer of resin on the inside before pouring the liquid silicone, and would have done it it didn't mean a further 12 hour delay to allow the resin coating to cure. I'm always rushing things, which is my downfall.

The centre is still not dry as of this morning, so it's going to be a good few hours to see whether my cunning plan has worked.

Made a mess of my attempt to rejuvenate the genuine lampshade, but I'm sure I can fix that. I did, however, mix some remaining liquid silicone with some red resin as an experiment, which produced a rather nice, necrotic, internal organ, or a tumour, from something very dead.

The silicone has given it a nice squidge, like a real tumour.

Now, here's something I learned from YouTube. Apparently, you can make very good silicone molds using common or garden silicone sealant mixed with talc. You mix it into a putty-like paste, press whatever you want to form a mold of into it and leave it to dry. I might try that with the good half of the clay former in order to create the other half out of resin. That's going to have to wait till next weekend though.