Dancing again

Earlier this week in Another Dance? I posted about some new work, which was really my opportunity to finally finish something started back in 2008.  In that post I'd got as far as making some cardboard models - to be used for mould making.

Well this photo shows those cardboard models set up ready for casting in silicon. 

I've previously used gelflex for shallow relief casting - but think I may have been converted to two-part silicon.  It holds its shape better, isn't so bubbly and gives a harder, stronger final mould.  The one major drawback is the price - because silicon can't be melted and reused like gelflex.

The walls for the mould are slices from a drainpipe, and these have been sealed at the base with clay.  The blue sheets underneath the mould are sticky back plastic - to prevent the cardboard lifting away from the board.

Here you can see the three silicon moulds, ready for casting themselves. (In a delightful shade of mint green!)

Again, I've used sticky back plastic to keep the silicon from floating away.  But instead of drainpipe, the walls for these moulds are slices of postal tube. I varnished the inside with a quick layer of shellac - so that the plaster wouldn't weld itself to the card.


Once sealed with clay at the base, the silicon moulds were then ready to be cast in SRS glass (a plaster-based investment) - which I buy from Special Plasters in Birmingham.  This has the necessary additions to reduce the likelihood of the mould cracking and failing at high temperatures.

This photo shows the final investment moulds once they've been released from the cardboard tube - and had the silicon removed, of course! I then went on to make a second set of investment moulds.

Once I'd finished the moulds, I left them to air dry for a couple of days.  Then came the firing:

Here you can see the six moulds set up in the kiln ready for firing.  I cut six pieces of fibre board (specially designed to survive kiln temperatures), and  cut a hole in each with a pastry cutter.  It works...but don't use it for pastry afterwards!

The pieces of board are then placed on top of each mould, to support small earthenware plant pots - which hold the lead crystal casting glass.  Once the glass reaches casting temperature, the glass melts and drains through the hole in the bottom of the plant pot (and the hole in the board) directly into the mould.  

Because I'm working with geometric shapes, it is possible for me to calculate the volume of glass I require relatively accurately using mathematical formulae.  In this case, the formula for the volume of a cylinder (πr² x h).  I can then multiply the volume by the density of my glass, to work out the weight of glass required.  I usually use Gaffer Glass, which has a density of 3.6g/cc.  There are other ways to calculate how much glass you need which don't require as much (if any) Maths!  I clearly just need to torture myself..!  You then need to add a little extra "for the pot" - as not all the glass will manage to drain through.

This final shot shows the glass after firing and removing from the mould.  You can see at the edges that the glass isn't shiny where it has touched the mould.  It needs to be polished.  With lead crystal you have the possibility of using hydrofluoric acid to polish - though some smoothing with a diamond pad may be required first.  I don't work with the acid myself, but take my glass to a commercial crystal company who will dip small pieces.

Well that deals with the glass side of things - but I still haven't covered the laser cutting!  I'll have to do one more post later in the week... Bye for now!