lately i've been experimenting with different methods of "holding up" the metals. Tradition dictates a mix of Pitch oil and plaster of Paris, but that seems ok for smaller bits like jewellery. Not so good when i need a 12" bowl full. Plasticine works well but its hard work to get it moulded in and if you loose patience and heat it up n the oven (sorry wife!) it gets very hot and painful to use and also looses some of its mojo after a few times, it goes all crumbly and nasty. I thought about it and resolved to add Vaseline/patrolium jelly as its basically chalk and jelly anyway. Its hard to mix, even the wife's Kenwood mixer eventually threatened to burn out. And its hellishly sticky when mixed rather too soft too. and When i used it it glued itself to the bowl with some tenacity. I had to scrub like mad to get it off. Pitch can be expensive and hard to get hold of. Seemingly in the Uk anyway, its not the roofers pitch usually but fancy Baltic pitch that's softer and its mixed with various things to make up bulk. I chanced on a web site that mentioned beeswax and plaster mix for the job, so thinking laterally. beeswax =expensive, ordinary wax cheep. i searched for wax on the net and found this site. http://www.exmoorcastingsupplies.co.uk/casting-store.asp?dept=35 thinking that modelling wax seemed ideal. However a phone call to the guy changed my mind he thought that wax would shatter when hit so recommended a more robust wax used as "sprue" for "lost wax casting". This stuff http://www.exmoorcastingsupplies.co.uk/casting-store.asp?dept=37 and rather impressively he was able to work out just how much would fill a bowl USING MATHS! (i could have with thought but would probably ended up just filling one with water) Anyway as i type i've melted some and a copper bowl is sitting full to the brim in the kitchen awaiting my punches.
The advantage of wax is that it melts easily (at about 60 to 70degrees) Pitch is messy and melting it out of the horribly easy to melt pewter didn't appeal. Lets see ah!