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Delft casting of flat thin objects


#1

Hi all, I have bought a Delft kit and tried a couple of time to cast
a pendant model I have. I probably picked one of the more difficult
things to start with, i.e. thin. Using this method the sprue comes in
at a right angle to the fairly thin piece. The model is around 1/8"
or a bit thinner. I made the sprue fairly large (1/4" or so), rounded
the corner where it joins the model, and added vent holes (and
otherwise folowed the directions and other tips I have found on
Orchid posts). Tried a couple of times but no complete cast yet. I
know other have posted on this subject before. My specific question
is: has anyone tried making a split sprue? That is, having the sprue
split and angle out right before it meets the model. That way it
wouldn’t come in at a right angle, and since there are two sprues the
silver wouldn’t have as far to go. I realize it might be tricky to
make this sprue arrangement in the Delft clay, but still it might be
worth it. I am casting Argentium silver grain from Rio, using a pinch
of borax for flux. Another idea i had is to perhaps pull a bit of air
through the vent holes to assist the silver flow. Would this work?

Todd Welti
Living Color Opal and Intarsia


#2

Hi Todd,

I have been using Delft Clay for about six years now with very good
success (Mostly Gold casting). You can use two sprues depending on
model’s shape. However it is tricky and time consuming. I have found
that wheneve I do not get a complete cast, it is due to lack of
adequate ventilation. Try to make your ventilation holes about 1/4"
from the object perimeter and regardless of the instructions that
accompanies the clay, I make ventilation holes all around the object
evenly spaced as close as permissible. Given the fact that your
metal is at proper temp prior to pouring, with additional
ventilation and by tilting the clay ring toward the end of the cast
you will have better results. I have casted pieces that are 2.5mm
thick by placing a flat piece (a file) under the clay ring to create
a tilt toward the end.

Hope this helps.
Jim Karjoo


#3

I agree with Jim about the extra vents. Though I’d add that while I
put in several vents around the piece especially opposite the (5mm)
feeder sprue, my vents are tiny - made by pushing a piece of 0.8mm
wire through (a piece of stg earwire). Fumes escape but very little
metal goes up the vents. Very little clean-up afterwards.

Maybe you could try a really short feeder sprue, say no longer than
10mm. That’s where the metal cools off a lot, going down the feeder
made of room temp clay.

If this is your first casting, why not do yourself a favour and try
easier shapes, to have some fun and to get some experience with the
technique.

Brian
Auckland NEW ZEALAND


#4

Hi Jim, what do you mean tilting the clay ring toward the end? My
sprue comes in at the center of the (flatish) model, so which way
would I tilt it? Have you ever tried actively ventilating - that is
drawing a modest amount of air through the vents? Also, if you make
so many vents, doesn’t it take long to clip off all those bits of
metal and clean it up afterwards?

Todd Welti
Living Color Opal and Intarsia


#5

Hi Jim, what do you mean tilting the clay ring toward the end? My
sprue comes in at the center of the (flatish) model, so which way
would I tilt it?

Regards,
Jim Karjoo


#6

what do you mean tilting the clay ring toward the end? My sprue
comes in at the center of the (flatish) model, so which way would I
tilt it?

Todd, I place my sprue at the end of piece specially for two sided
ob jects, hence I will tilt it toward the end for easier flow and
that elim inates the headache of cutting the sprue if its recessed.

Have you ever tried actively ventilating - that is drawing a modest
amount of air through the vents? 

No, haven’t had the need to do that.

Also, if you make so many vents, doesn't it take long to clip off
all those bits of metal and clean it up afterwards? 

Cleaning up the piece takes about 3 to 4 minutes.

Regards,
Jim Karjoo


#7

So, even though the molten silver has further to go (since your
sprue comes in at the side) it is more than compensated by the tilt.
Correct?