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Casting a twig


#1

I tried to cast a small hollowed out twig, that was intended to
ultimately slide on a chain, and it didn’t cast well. I had a giant
spue and it didn’t look like there was any remaining ash inside
after burnout. But the casting looked like possibly the twig had
expanded and damaged the investment. The surface detail was all
gone. Anyone have any twig casting tips before I try it again? Your
help is very much appreciated! Thanks, Mark


#2

I’ve done a couple vines and organic things. Try a long burnout, 8
to 12 hr. Somewhere after the highest temp but before you cast blast
the opening with a can of air and put it back in the kiln then cast.
Try centrifugal If you have access to it. Mix your investment up to
maybe 7 minutes before pouring so gloss off is soon after pouring.
Good luck. SD. Organic things are porous so don’t expect the surface
to be perfect, might need some finishing.


#3
I tried to cast a small hollowed out twig, that was intended to
ultimately slide on a chain, and it didn't cast well. I had a
giant spue and it didn't look like there was any remaining ash
inside after burnout. But the casting looked like possibly the twig
had expanded and damaged the investment. The surface detail was all
gone. Anyone have any twig casting tips before I try it again?
Your help is very much appreciated! Thanks, Mark 

I’ve cast a lot of scorpions and palmet to bugs and always let them
soak in denatured alcohol for many months prior to taking them out
and letting them air dry before spruing. And I’ve never had luck
centrifugal casting bugs, it always required vacuum. I suspect twigs
are similar.

Paf Dvorak


#4

Mark,

Not sure if this will be helpful. I would not be surprised if
someone has a better suggestion, but this is what works for me when
I do twigs or other organics.

When I cast organic pieces, Once the investment shows a white clean
burnout, I vacuum (like with a 1 gallon shop vac) just in case their
is any ash residue, then put the investment back into the kiln for
about 15-20 minutes to make sure it is up to the required
temperature for the metal I am casting. It is a delicate procedure -
you cannot get the plastic vacuum hose or nozzle too close to the
hot investment - the suction is too strong, and any plastic parts
would melt. I have not cast hollow organics only solid.

I usually do a preliminary cast in silver, mold it, and create a 2nd
generation injected wax model which I then go in and detail, and /or
embellish with carving tools, or fuse any porosity - for some reason

  • 1st generation twigs seem to have micro-pitting or porosity - but
    not other organics (Like buds or seed pods or sea weed) - I am sure
    one of our more scientific colleagues, like James Binnion or Peter
    Rowe, will be able to explain this.

Good luck, Linda


#5

Ive don a bit of organic casting and for me drying and exchanging
super heated modeling wax (blue dentist modeling wax) has worked
well, I hold the kiln at 1350F for a couple of hours (1 for each
inch in diameter at least) and opening the door when very hot to let
oxigen in to help the ashes disapear, the vacum sounds good as an
extra safety specially with heavy pieces.

for embeding the extra hot wax I apply hot wax to the surface by
spatula andthen I bring a red hot tool almost in contact to the
piece to make the wax go IN to th piece making it water proof
(therefore investment proof)


#6

Hi Mark,

I cast twigs and organics a lot. What I have found is to coat the
materal with a clear acrylic or lacquer spay paint. Give it as many
layers as possible without loosing the definition. I would also cast
as soon as possible after investing. The key is to not let the
moisture in the investment to penitrate the pores in the organic
materal. This cuts down on swelling and porosity since the
investment does not get sucked into the pores of the organic.

I use 2 hrs at 300 deg. F, 2 hrs. at 700 deg. F, 4 hrs at 1300 deg
F. And 1 hr. At 1000 deg. F then cast. I only cast in silver.

Good luck


#7

and don’t vacuum debubblize!

Paf Dvorak


#8

I know it is more work, but making a mold of the twig and then you
could use a wax for casting. If the twig was wet/freshly cut, try
drying a good bit before casting to get moisture out of the wood, ,
for a couple of reasons. One, the moisture can expand too fast
(steam) and breakdown the plaster and 2 it will burn out
faster/easier. Also getting some air into the void while the
investment is red hot will help burn out material. I have never had
problems like you are having, so sort of shooting in the dark.

john dach


#9

I spray the organic with silicone spray and make vulcanized molds,
they are what I am used to for mold making. Shoot the waxes, use the
cast twigs to fabricate with. I made the molds, another person I did
casting for asked if she could use some, she has a whole twig
jewelry line.

Richard Hart


#10

You can also use a wax dissolved in a solvent to “water proof” the
casting without any loss of surface detail. I melt some foundry was
(candle wax doesn’t work too well, a very different molecular chain)
1 part then add a solvent, most often paint thinner, to the melted
wax (after removing from the heat source used to melt it, , FIRE
HAZARD!!!) while stirring. I use this mixture on all sorts of wood
items around the house, shovel handles, other tool handles, wooden
gates, anything I don’t want to paint but I want to keep from rotting
in the moisture. Heat the piece to be coated, hot sunny day is great,
and paint the solutions on. You will see it soak into the fiber
structure and waterproof it. It would be a fast application on a twig
and would not interfere with the surface detail. This works only on
dry wood. If it is freshly cut, I would use lacquer or some such.

john dach


#11

I appreciate all the tips! I did just seal my deck with a
transparent water proofing product. I think I will try some of that
to seal the twigs for next attempt. I also did vacuum the investment
the same as I would a wax. I will vacuum before I pour but not once
the twigs are invested. I’m looking forward to trying it again.

Molding does make a lot of sense.

Thanks again to all who replied!
Mark


#12

Like others have said- vacuum only the investment and pour
carefully. If necessary, I tap the sides of the flask to raise up
and pop any airbubbles afterwards. Ciao, Jo-Ann


#13

Hi Mark, Over the years, we/my students have cast many twigs. Here
are a few photos attached. We always seal with paraffin (melted,
dipped, hung up to dry)

You can also try some kind of sealant–varathane, hairspray,
furniture polish etc. But, you must seal !!

Anyway, you can google one of my former student-Emi Grannis. She
did/does quite a bit of this work…


#14

Jo Ann, your student’s cast twigs are gorgeous. How did you get rid
of the ashes when you did the burnout. It was suggested thatwhen
burning out twigs, one should take the kiln up to 1500 degrees, then
remove the flasks and dump out the ashes, then return the flasks to
the kiln, and drop the temperature to casting temp of l000degrees.

However, I wonder if the investment will hold up to 1500 degreesand
would appreciate advice before I try it.

Years ago I cast some “twigs,” that I made out of wax wires that, t,
carved with my exacto knife to look like a twig, and addedlittle
bumps and knurls with hot dripped wax. However, would like to try
casting real twigs, as nature does a better job at forming them than
I did using wax and an exacto knife.

Alma


#15

I’ve cast all kinds of organic materials. The drier/woodier the
materials, the more problems. On some I did some experimenting to
fill the porosity. I have a nifty tool that is a wood burning tool
from Michael’s. It’s a exact knife mixed with a soldering iron. It
was about $12. Using a medium (I like pink) injection wax on the end
of the knife, I have carefully used hot wax to fill the micro voids.
It has been successful in most instances to eliminate surface
porosity in the end piece. The wax bubbles into the surface if its
porous. Its obvious if there is going to be a priblem. Also on
thinner woody pieces I have been able to build up a surface and
texture to match.

I never used a vacuum cleaner or blast from a can of air. That would
help alot to clear out the ash residue. Thanks for that tip!

Eileen


#16

Now I know why these items are SOOOO freaking expensive when you try
and buy them to incorporate into your own pieces!!! I guess we must
literally “pay the price” when we cannot afford nor have the ability
to have the equipment to do this casting stuff on our own. :frowning:


#17

I am not sure if this method has been mentioned.

When I cast organics, I first sprue up heavily and then mix up some
casting plaster to a cream consistency and then paint the object with
it all over.

I use a soft small paint brush.

Then I wait until it starts to gloss over and I mix a little more
and paint it over again.

I do this about ten times.

I make sure that the coats have not completely hardened before I
paint the next one, otherwise they will separate during burnout.

Then I mix the rest of the investment, vacuum, and pour over the
sprued object.

Then I dry the mold out in the oven for about six hours at 100C to
eventually 300C.

The slower the better, the mold must be completely dry.

Then I ramp up to 800C and keep it there for 3 hours.

Then I cast at 700C and I use a spin caster and I wind it up an
extra turn from normal.

(Normal is 2.5 turns and normal casting temp is 500C.)

Don’t believe the yada about sulfur contamination, it’s BS.

Then I quench the mold in water.

Here is a picture of an insect that I cast.

Note the feelers and the fine detail that can be achieved.

The insect is unmounted at the moment, so that’s why everything is
folded back and the legs inwards.

About 70mm in length.

meevis.com


#18

Hans…this beetle casting is incredible. I was involved in casting
flora and fauna at a museum years ago for a diorama on early
Florida. It was one of the most interesting projects I was ever
involved with in a museum. I got all kinds of ideas for jewelry and
got paid too!! :slight_smile:

Chris


#19

An alternative to casting. metal clay. It is possible to paint
layers of metal clay Slip on twigs to reproduce individual twigs. Of
course, each twig is one of a kind and this may not be what you have
in mind. But, it works.

Minimum of what you need: twig, metal clay Slip (commercial or
homemade), watercolor paintbrush, metal clay kiln.

Just a thought,
Linda Kaye-Moses


#20

Hans that cast beetle is just real looking down to the feelers and
detail, that I fully expected it to open his eyes and wink at me.
Absolutely wonderful. Thank you very much for sharing the
as to how you made him/her. You have granted that little
creature immortality. Alma