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More Questions about Delft Clay


#1

I’ve been scouring the archives for tips about casting with D.C. and
found some wonderfully helpful suggestions. However, I have two
questions to which I could not find an answer.

  1. What is the best way to determine how much metal (I will be
    casting in sterling and/or fine silver) to melt for the item itself
    and the sprue button if the model is made of sterling, plastic,
    fimo, sculpy, or any other material? Are there any guidelines that
    could be applied?

  2. From what I read, it seems that beginners have the most
    difficulty with getting the hot metal to pour past the sprue channel
    so that it does not get into the piece itself. Someone suggested
    putting the canisters into a 200-300 degree oven, but it was not
    clear when this could be done. Would it be helpful (or even
    sensible) to put the canister on a small ultralight kiln (that’s
    what Rio calls them) while pouring the metal? That might help to
    keep the bottom part of the assembly hot–has anyone tried this?

Thank you all for the wonderful and help–it is really
awesome. Sincerely Sandra


#2

Delft clay is really easy to cast into.

The simple way to ascertain how much metal you will need is to fill
a narrow container about half full of water and make a mark where the
water comes to. Drop in the model and make a new mark. Remove the
model and then add metal to the container until the water reaches the
upper mark again. This will give you the amount of metal for the
actual object. Simply add about half to one whole ounce more for the
melt. That should give you sufficient to fill the sprue and the
button. Obviously if you have a much larger model add a little more.

Getting the metal past the sprue has nothing to do with the heat of
the mould! It’s all about making the sprue itself wide enough. Use a
drill bit of the correct dimensions - as a beginner it would do no
harm to use one a little wider. You need sufficient metal to fill the
mould, the sprue and the button (the button acts as a reservoir and
as a weight to push the metal into the mould.)

Remember to always make the sprue by inserting the drill bit from
the INSIDE of the mould to the outside, clean up the junction between
the bottom of the sprue hole and the gap in the mould (the place
where the model was) by compacting the sand with a small dapping
punch!

Reckon on getting about 70% successful castings.

Tony Konrath


#3
What is the best way to determine how much metal (I will be casting
in sterling and/or fine silver) to melt for the item itself and the
sprue button if the model is made of sterling, plastic, fimo,
sculpy, or any other material?  Are there any guidelines that could
be applied? 

why not make a wax sprue about the right size, adhere it to your
piece, then use the ancient Archimedes technique- put it in a glass
of water, and mark where the water rises to. Take it out, then add
silver to the water till it reaches the mark, and maybe a tad more
for your sprue button. Remove the wax, and cast as usual.
Anne Stickney


#4
    1. What is the best way to determine how much metal (I will be
casting in sterling and/or fine silver) to melt for the item
itself and the sprue button if the model is made of sterling,
plastic, fimo, sculpy, or any other material?  Are there any
guidelines that could be applied? 

My brief encounter with the delft system tought me that if you melt
more than you think is needed and pour out the rest into a water
bucket, its less trouble than determining weight needed.

   Someone suggested putting the canisters into a 200-300 degree
oven, but it was not clear when this could be done.  Would it be
helpful  (or even sensible) to put the canister on a small
ultralight  kiln (that's what Rio calls them) while pouring the
metal?  That might help to keep the bottom part of the assembly
hot--has anyone tried this? 

I have tried placing the finished mold in a toaster oven @ 300F for
20 minutes and it helped alot, I stopped getting part-fills. As for
your idea of using the Ultralight kiln there might be a problem with
over heating the bottom of the mold and it might burn the clay. One
suggestion was to make the sprue a minimum of 5mm in diameter, and
vent vent vent! I’ve had much more success pouring gold using the
delft clay for some reason. Keep in mind that gravity will only do so
much.

Hope this helps.
Jonathan Brunet
Montreal, Canada


#5
 One of the characteristics of the delft process is that it
requires a large diameter sprue hole. About 1/2" seems to work well
for most smaller items 

To throw another couple of cents worth in… I’ve done (and taught) a
fair amount of delft or sand casting, and have found it very helpful
to preheat the assembly. Probably, with a large sprue and fairly open
form, this is unneccessary, but I mostly cast twigs. Without the
preheat, it is difficult to get the silver to travel all the way
along. I would also reiterate the importance of venting. If your vent
is angled upward, it can be as large as you like-- the silver is
disinclined to reverse direction, but air doesn’t mind. The friend
who first taught me the technique was told by her instructor to think
of the pour as a “little silver car”. The little silver car likes
smooth, unconstricted roads, and can’t make hard turns very well. I
find this helpful! May your little silver car run like a dream!
–Noel