I want to produce some cast pieces from some objects I have, they are basically like cogs or gears, but some are very decorative. Some of the larger ones are very delicate in places with spokes possibly about 1mm wide, maybe slightly less. These particular ones are about 40 mm in total diameter so the delicate spokes are quite long.

I was thinking firstly about mould making and using PMC, but I have found problems with removing them from the moulds, if I let the pieces dry completely they are brittle and prone to breakage, and if I try to remove them when the clay is still wet, it's nearly imppossible not to irrepairably deform the moulded piece. I had some success with a less decilate cog/gear but I think I have messed up the firing or something as when it came out of the kiln it was quite brittle, and now it's in bits!

Anyway, these issues started me thinking about Delft Clay, but this has given me a couple of questions to answer as someone who's never used it before.

I'm concerned about a suitable area on which to position the sprue - I can probably get away with this though as there is a less delicate part on most of the cogs. My main concern however is will the silver flow into all of what will be very delicate and narrow channels in the mould. It will need to go through these and out into the far less delicate frame, so a lot of silver will have to pass through them.

One thought I had was to maybe have two sprues, and therefore 2 points to introduce the silver, but then I guess there would be issues with silver poured through the 1st hole setting before the 2nd hole is poured?

Any thoughts or ideas on this would be appreciated!