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Delft clay casting problem


#1

Hello,

I have been attempting to use delft clay to cast a small replica of
a shield about the size of a 50p but a bit thicker. I having tried
several times now and I am only getting a half filled cast, good
detail but only on the half that it can reach. I have tried adding
more air holes for the air to escape and changing the position the
silver enters the mold but still no luck. I wonder if I am not
poring fast enough, it seems to be solidifying in the funnel to
quickly, any help would be great


#2

Ah, Rachel it sounds like you are removing the torch from the
crucible too far in advance: Keep the metal rolling in the well
glazed crucible (borax glazed) up to the pour. Its a bit tricky when
aiming for the inlet into a mould but you will get the hang of it.
Rather than using precious metal whilst earning try using a cheaper
alternative like "merlin’s gold"a jeweler’s bronze with similar
properties to 14 kt and sterling in temp. and workability time. Also
check to make sure the clay you have is moist enough-compress a
handful and if it conforms to your hand after you open your fingers
its right- if it crumbles or does not hold shape its too dry- work
in a bit of lightweight oil or glycerine to the clay and insure its
evenly dispersed without clumps, and then sift it or sieve it to make
sure its as fine as possible when packing it into the cope. If you
have a copy of the Complete Metalsmith, tim McCreight covers the
process and problems in the book-most libraries have it on the shelf
if you don’t! Any questions feel free to contact me off list. rer


#3

Try a larger sprue hole and more melted metal. The only energy you
have to move the metal before it solidifies is gravity acting on the
mass of melted metal. The nice thing about Delft is that you can
keep on trying until you get what you want. Post your solution and
finished piece. Rob

Rob Meixner


#4

Try to pour both hotter and faster. What is your metal? Perhaps you
could make your model thicker? Add some wax on the back/inside?

Mlou Brubaker


#5

Two suggestions-- Bigger gate to pour through; pre-heat the sand
mold.

I heat my ready-to-pour mold to maybe 400F or so, when I have the
patience or the need. It helps a lot!

Believe it or not, I also use a centrifugal casting machine the get
the silver into the sand, too. I don’t wind it up too much, but I’ve
never had a single problem doing this. I am using the sticky sand
sold for sand casting and a square frame (the kit Indian Jewelry
Supply and others sell).

And I wouldn’t do it without that nice tall shield around the
centrifuge.

YMMV!
Noel


#6

I am NOT an expert with this, but do use the delft clay, so will
share the errors I have made :slight_smile:

LOTS of air holes! Be SURE you have at least one at the end of every
single protrusion!!! VERY important!

REALLY think about orientation, and where you will pour from - this
makes a huge difference too. I’m not good enough yet to say “do
this” but I have found that if it doesn’t fill properly, and I’m
sure I have lots of air holes where I need them, sometimes changing
where I pour into makes a difference.

Next, make your pour hole HUGE!!! Really - WAY bigger than the
instructions say!

Make sure you also have way more melted metal than you think you
need, and that you arrange your work space so there is as little
space as possible between where you heat and where you pour. I
finally arranged fire bricks around mine to help hold the heat in,
and found that really helped. made almost a little fire brick "oven"
with a top and sides…

Then be sure you keep the heat on the crucible while pouring.

Hopefully someone who IS an expert can chime in with more helpful
tips!

Beth Wicker
Three Cats and a Dog Design Studio
http://www.bethwicker.com


#7

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
it…

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).

good luck,
Rick


#8

Here are some pictures that might help.

Hans


#9

Thanks Hans,

You do such an excellent job with your photo sequences. I’ve done
steam casting, and even though it is pretty cheap to do, it takes
TIME. Delft clay casting appears to be much faster. Good to have
another tool in the tray.

Judy in Kansas, where the moon is full and the air is clear - night
time shadows are amazing.