I cast with Delft Clay all the time and have for over 4 years.
I agree with everyone saying you need a large enough funnel for
pouring the melted metal in and you need lots of air holes. I highly
recommend you watch the free jewelry instruction video by Andrew
Berry. This is a free youtube video so if it's allowed on the forum
rules, here is a link.
Watch all 3 parts of the video. It gives you a good idea on how to
make the funnel and air holes. You may remember that a few weeks ago
I asked about the stand up square kind of sand casting frame. If you
purchase that frame it will give you much more options for casting.
The round cylinders they give you in the kit are limiting the kind of
things you can cast.
Basically, you can cast simple things like pendants and earrings
with the cylinder frame they give you. But if you want to cast
slightly more complicated shapes like rings you should get the square
frame for sand casting.
But back to your question about not getting a complete cast with
You need at least 4mm opening for where you pour the metal into the
delft clay, and you need, in my opinion, 6 to 8 different small air
escapements or 4 large ones. It's easier to just make small air holes
because you can just stick a share burr into the Delft clay and then
drag a "runner" hole to where the model is. Again, what the kick ass
video by Andrew Berry.
That guy is a great teacher.
I also agree with my fellow Orchidians that you may not be keeping
the flame on your pour up to the last second. I always make sure I
heat up the top side of the crucible where my molten metal is going
to pour out of. If you don't, the cooler part of that top crucible
spout is sucking all the heat out of your molten metal.
I love Delft clay casting. I find it extremely inefficient to stick
a small flask in a kiln and burn it out for 6 hours just to make a
small piece of metal. I'll never understand why we can't develop a
more efficient way to cast jewelry. I have not read up on it yet but
I assume induction melting/heating is the faster more efficient way
but the irony there is that it's even more expensive than a power
bill for a 6 hour burnout. I wonder if this is why many jewelers
simply outsource their casting work as even I am considering going
this route as I expand. Unless I can perfect steam casting and using
a DIY kiln set up.
Yes there is normally more finishing work required for the Delft
Clay castings, but if I control the amount of oxygen correctly, I get
no more porosity in my pieces than when I use other casting methods.
There are limitations to the amount of detail I can get with Delft
Clay, but for many of my designs it works beautifully.
Just make sure your hole is at least 4mm, make sure you metal is
really spinning and liquid, and keep the flame on the pour (and
pre-heat the edge of your crucible as or before you are pouring), and
you will get good castings. (Don't forget good air escapement and use
more metal than you need for the model because like everyone is
saying, you need gravity to push your metal into the voids).