We have used the Delft Clay casting method for a couple of years
now. The most important thing to remember is that gravity pulls
the metal into the mould so the sprue can not be too thin nor
long. A diameter of 3mm, nothing smaller.
Air vents are important, we put 4 or 5 in with thin channels
coming off the mould, you can always cut them off should the
metal flow into them.
If you are trying to cast rings them make sure you wiggle the
ring slightly to enlarge the shank area because if it is too thin
then the metal solidifies before it has had chance to flow .
Put the sprue into the mould where there is the largest cavity
again so the metal does not freeze too soon.
When melting the metal keep it molten for at least 30 seconds.
This seems to be the minimum time so the metal gets up to a good
We have cast a ring of 1 1/2 oz.
This method of casting works well for us, because we usually
make one off pieces. We usually make up a master in wax or wood.
Providing the clay is compacted well you can get very good
definition. We have cast a small shield with the original having
engraving on. The detail has really good.
I met the gentleman who has patented this casting system a few
years ago in a trade fair in the UK. He gave us answers to the
problems we had using this system and they all worked.
If I can be of any further help them please feel free to mail me