Monday, 10 May 2010

.... And they're back (with lots of news!) part #1

Well, the last few visits to the casting shack have resulted in a plethora of work and some frenzied mould making, plinth carving and general fettling!

First off, the complex skeleton piece mentioned below is cast, fettled, polished and resting on a nice piece of honey coloured bath stone (cheers Bryn!). That was the complex polystyrene piece which featured in an earlier posting. The skeletal pieces I've cast before were produced in individual pieces which were cast separately and then threaded together along a piece of threaded bar which ran down the spine. This time however, I glued the vertebrae together with the ribs, creating a single piece. This was a bit unusual, but as it was a smaller piece, I thought I'd avoid the faff of lots of tiny elements - though with other attendant risks. I've noticed in a couple of pieces recently (notably the sword hilt - more to follow) that there is a natural weakness along the line of where separate pieces of polystyrene are glued together - and 'gaps' in the glue allow sand into the joint which then creates a stress-line and potential fracture point in the cast...

I attempted something entirely new with the casting of this piece. As usual, I'm running low on casting sand - so in attempt to get what remains to run a bit further, I used some lumps off of old moulds to act as 'plumbs'. Its something I picked up from building site work - to make concrete go further, workers would often tip/mix large lumps of hardcore into the concrete mix (if this is totally against building regs, don't blame me!!!). In the case of the mould for 'Shelleton' it saved an inordinate amount of sand - PLUS by having a solid core (which I shaped to math the pattern), it reduced the amount of warping/deformation of the polystyrene whilst I packed the sand around it... I'll post some pictures, and hopefully this'll illustrate the point...


Here we go - shaping a bit of an old mould to fit underneath the polystyrene..


... and adding some 'plumbs'...!


... and packing in and around with sand. I did this in two layers - one up to mid way and a final one 'over the top' with pour-ins and vents to act as a cap...


... as I said, a fairly complex mould - but one which poured nearly perfectly. The two cylinders are the pours (glad there was two - only one worked properly!!) - and the drinking straws are the vents) The only imperfection was that slight distortion of one of the ribs - caused by the packing process and the tendency of the polystyrene to flex...

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