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Casting in tuffa


#1

Was: Ethics of Learning & Teaching

Photos on my blog 

Nice solution, and nice blog, Lee! Are the conchos (etc) cast in
tuffa? I’m planning to try that some time soon. Any tips?

Noel


#2

Hi Noel,

My conchos are carved in blue ferris file a wax. Check out the
following for my method:

Items cast in Tuffa stone have a very textured surface.

In tuffa stone carving the design is cut into the stone whereas in
wax carving the background is cut away.

Lee Epperson


#3

Hi Noel,

My conchos are carved in blue ferris file a wax. Check out the
following for my method:

Items cast in Tuffa stone have a very textured surface.

In tuffa stone carving the design is cut into the stone whereas in
wax carving the background is cut away.

Lee Epperson


#4
Items cast in Tuffa stone have a very textured surface. 

Yeah, that’s why I thought maybe that was what you’re doing. The
background on your pieces appeared textured to me, the freground
smooth. I was in Phoenix briefly this spring and saw Native American
pieces at the museum, done with tuffa, that looked like that.
Presumably the high areas are ground and polished.

My advanced class and I have been having a great time exploring
primitive casting methods-- sand, cuttlefish, and the fast organic
methods where you pour silver into/over water, straw, salt, even
peas (all I am saying is give peas a chance…)

It has been really fun and interesting, and tuffa seems a logical
next step. I thought Rio carried it, but I don’t see it in the
index. I think Indian Jewelry Supply has it. Anyone have a better
source? Or a text?

Noel


#5
It has been really fun and interesting, and tuffa seems a logical
next step. I thought Rio carried it, but I don't see it in the
index. I think Indian Jewelry Supply has it. Anyone have a better
source? Or a text? 

Lonnie’s here in Phoenix carries it 602-220 0494. It isn’t on the web
catalog and I don’t know how much it is and shipping, but I use it
in every casting class I teach. It’s fun stuff.

Joan


#6

A question was asked regarding tufa. this has been
posted on Ganoksin previously and I am just pasting it in; I have
contacted him, but I wanted larger pieces to cast into than he has.

  To all silversmiths and gold smiths: 

  I am proudly announcing the debut of my company, AAICA LLC! 

  At the present time, AAICA's main product involves working
  with Tufa as a casting aid for casting silver, pewter, and low
  temperature alloys. 

  What is Tufa? 

  Tufa is a naturally occuring rock that from fossilized
  volcanic ash. Molds created from this material are the historic
  method for silver casting used by the Navajo (Dine') people
  residing in portions of the Southwestern United States. 

  AAICA LLC resides in Apache County, Arizona, very close to the
  eastern border of Arizona, where a lot of the Navajo jewelery
  activity takes place. 

  AAICA hopes to relieve some of the thankless drudgery involved
  on the part of those Navajo silversmiths who would rather
  design and use molds than cut them. AAICA would also welcome
  anyone else interested in supplementing thier cuttlebone or
  investment casting with Dine' methods. 

  Anyone familiar with cuttlebone casting can easily make the
  transition to casting with Tufa. Tufa therefore presents
  advantages over using cuttlebone: 

  1) Larger molds can be created out of Tufa blocks than
  cuttlebones. 

  2) Using Tufa instead of cuttlebone can help conserve oceanic
  ecosystems. 

  3) Tufa presents an alternative for people who have religious
  or philisophical objections to using animal products as a part
  of crafting. 

  Tufa also presents advantages over the lost wax casting
  method: 

  1) Like cuttlebone casting, TUFA is a far "lower-tech" method,
  requiring less expertise and less money for the beginner or
  small crafter to begin using. 

  2) The pure silica particles comprising many investment powder
  are far more hazardous to inhale accidentally than the
  particles from Tufa rock. 

  AAICA can take 2D or 3D images or artwork to: 

  1) cut and square TUFA blocks to order for freehand artists 
  2) produce a catalog of off-the-shelf shapes 
  3) creating molds to 0.01 inch accuracy using a 3 axis CNC
  milling 

  0.01 inch accuracy is all that is typically needed by the vast
  majority of cuttlebone and TUFA users who presently work by
  hand. 

  BobCAD, BobArt, and Python are used for generating the
  necessary Gcode. The Gcode is executed on AXIS running under
  Ubuntu Linux with the Magma real-time kernel modification. 

  I will be on summer vacation between 10 June and 25 July, but
  I will be happy to take bids for later jobs over this period. I
  will also be very happy to entertain any or all suggestions or
  requests by potential customers and other interested parties. 

  Sincerely, Andrew Jonathan Fine, Owner, AAICA LLC, aaica.com

#7

FYI the AAICA web site, and presumably the business, is defunct.


#8

Hello all

I am hoping someone can give me some advice, or send some photos. I
am doing Tufa stone casting, and having problems doing larger scale
items such as bracelets, and belt buckles. Small items work fine,
but the larger pieces - the metal stops about 1/3 or 1/2 way into the
mold. I am venting, so not really sure where the problem lies.

Any advice?
Aries


#9

You need to preheat the tufa stone… I cast a large bracelet eons
ago with and Indian Artist at the Heard Museum. He preheated both
sided of the stones and then tied them together with strips of
bicycle inner tubes. Then preheated again, before pouring… Hope
this helps…

Joan


#10

Hi Aries,

My suspicion is the metal is solidifying before it totally flows
into the casting because the mold is too cold. If you are not heating
the mold, you might try heating the mold in a kiln in the 900 - 950 F
degree range. This is what is done in lost wax casting. If you don’t
have a kiln you might try an oven as hot as you can get it.

Preheat the mold for at least an hour not just a few minutes.

I hope my humble advise helps,

Ken Moore
www.kenworx.com


#11

This is no trivial task. I just completed a belt buckle where the
finished weight was about 125 grams. It eventually required about 8
oz of sterling to get it cast. When you say venting, I hope you mean
vents that are at least 1/4 wide and as deep as the carving; there
better be a lot of them. You need a lot more silver than you think
because you should expect silver to come out of the vents; you don’t
want to run short. I did restrict the vent carving at the very exit
by about half the vent’s cross-section to limit the amount of spew.
If your piece is open design (like a Navajo buckle) your carving
should include several vertical sprues connecting the carving
elements. Don’t get hung-up that this apparently destroys your
design, you saw them out later. That’s why you’re a sliversmith. I
had to resort to sprues on the back side of the mold as well as
preheating the mold to about 500-600 F prior to casting. Lastly it
helped to add a tiny amout of zinc to the molten silver. By tiny I
mean I used 1/4 of a US penny (minted after 1982). It imparts a
change in viscosity that makes the sterling a bit more "slippery"
while not completely misrepresenting the 925 alloy. Be patient. It
took me 4 tries to get a complete casting.

You may discover that parts of your carving break over repeated
attempts. You can repair the damaged areas by creating a slurry of
finely ground tufa in a 30% solution of sodium silicate. Pre-wet the
area with some 30% solution itself then apply the slurry with a
dental applicator or palet knife. Let dry and recarve the area. You
may have to experiment with the sodium silicate concentration; too
much and it’s too hard to carve, too little and it crumbles. Hint:
You find sodium silicate at a pottery and ceramic supply shop.

Good luck, post your results.

RC2