Iron lintel – mould making continues

The silicon mould and plaster mother mould that I took on the headland at Clachtoll made it safely to the Scottish Sculpture Workshop for the next stages.

Firstly I re-constructed the plaster mould so that I had one complete cradle for the silicon. Then I pinned the silicon into the plaster support mould and coated the inside of the mould with wax. I stippled the first layer on to capture the detail and and subsequent layers were brushed on to build up a firm mould a centimetre or so thick (thicker at the top edge) I then built the wax up as far as possible to remove undercuts on the inside.

I removed the wax wax from the silicon ready to start taking the resin-bonded sand mould.

I built a temporary box and used petrobond sand to build up the base to the wax. I did not do a good job on this, so had to make extra mould pieces at the penultimate stage (note to self to do better next time).

The resin-bonded sanded is mixed and rammed into the box around the wax, taking care to avoid undercutting.

When the top part of the bonded sand mould was complete the whole box was turned and the ‘rescue pieces’ added. The base of the mould could then be made.

This makes a particularly uninspiring photo (above), but it over took a week to get there.

The mould came apart as planned and was built up into the base and the top parts. I cleaned the joins: Michael (SSW’s assistant technician) helped with the core wash; I found the bars to hold it closed and Eden (SSW technician) working with George Beasley drilled the pour holes and air vents; the piece was moved outside; the cracks were glued; the pour cups glued on; the clamp bars put on and it was ready to pour.

Unfortunately I only have video footage of this stage so I can’t show it. The next post will show the pour.

Stone to Bowl clay dip moulds; incl wax melt out and all-in casting

Returning to Stone to Bowl:-

Once the wax models have been made and sprued they are then dipped in a slurry mix of clay (this time from Kingsbarns) sand (Cellardyke beach) and fibre (horse poo from near Kilrenny). There are two mixes, one is fine and the early coats are done in this and the other is coarser to build up the outer layers. Each layer has to dry before the next layer is added so it takes several days to build up the mould.

When the mould is built up a clay funnel is added. The moulds are then ready for the wax to be burnt out. The first photo shows the burn out. Below are the moulds that have been burnt out.

The link below is to an animated film about lost wax casting, which explains the process well.

https://hyperallergic.com/286780/an-animated-guide-to-the-bronze-age-technique-of-lost-wax-casting/

I also tried out a casting method where you burn out the wax and then put the copper alloy in one end of the mould. You then seal up the mould with a lid and clay mixture and return the mould to the furnace.

This photo shows the moulds and lids ready for burn out.

This photo shows the all in one moulds ready to return to the furnace for the copper melting stage.

In theory the copper heats to melting point and you upend the mould and the copper pours into the part that you want to cast, In practice because you can’t see the metal it is difficult not to either get incomplete melting or over heating and the metal seeping out through the ceramic shell.

The photo shows incomplete melting, the copper is fused (bottom right)

This photo shows a mould where the metal over heated and seeped through the mould walls. There are two moulds, one complete (but rattles so I’ve not broken it) and an open one.

The moulds with incomplete melting can be ‘re-used’ as open moulds.