This is my first post to this forum and I hope someone here can help
me as I am thoroughly frustrated and nearly blind from reading
through archives all over the Internet, trying to find a snippet of
I read who-knows-where, a while back.
Someone posted in a forum or wrote in an article that they used a
common household alternative to alumina hydrate or vermiculite to
support PMC pieces and keep them from slumping in the kiln. It was
either baking soda or baking powder, I think, but I can’t remember
for sure and don’t want to cause any damage to my new programmable
kiln or my PMC pieces in my ignorance. Has anyone here used or heard
anything about the use of any kitchen-cupboard substances for this
purpose?
For the record, this is more a matter of availability than a re-hash
of the safety issues. I know that asbestos-free vermiculite is
available these days. I just don’t know where. So, if there is no
readily-available household alternative to be had, then can anyone
tell me where, exactly, I can procure either vermiculite or alumina
hydrate in small quantities (5 lbs or less), either locally in the
Phoenix, AZ metro area or on the Internet? I am googled out and any
help would be sincerely appreciated!
Vermiculite is typically available at gardening supply stores, as
that’s where it’s primarily used. In terms of the other
kitchen-cupboard stuff, I can’t help you as I don’t do PMC. Sorry!
Karen Goeller
No Limitations Designs
Hand-made, one-of-a-kind jewelry www.nolimitations.com
Someone posted in a forum or wrote in an article that they used a
common household alternative to alumina hydrate or vermiculite to
support PMC pieces and keep them from slumping in the kiln.
Not sure this is what you mean, but I use silica sand. The aluminum
hydrate I have is as fine as flour and gets all over-- silica sand
is larger and stays put. I used stuff in a bag, nice and clean for
ceramics, but washed sandbox sand should work just fine too.
Someone posted in a forum or wrote in an article that they used a
common household alternative to alumina hydrate or vermiculite to
support PMC pieces and keep them from slumping in the kiln. It was
either baking soda or baking powder,
I think it was baking soda, though I am not positive.
Vermiculite, if you can’t find it in a garden center, can be
purchased online from Uline (large quantities) or Whole Lotta Whimsey.com (small quanitities).
You can also use perlite, which since it is used for indoor plants,
is easier to find year-round.
I can’t answer your specific question, but I can point you to a
source for small amounts (5-10lbs) of alumina (either calcined or
hydrate); try a good pottery supply house, you know the kind of
place you’d go if you needed an obscure kind of clay or glaze. They
usually carry alumina and silica (a bad alternative choice!!!) in
the required powder form. Not being a potter I don’t know what
potters use alumina for, but I use it in my glass molds…
Tonya at Whole Lotta Whimsy carries small quantities of vermiculite
and even has a great dish to use it in. They’re right next to each
other on the Firing and Torch Supplies page in case the link doesn’t
go through.
I put the question to the metal clay Yahoo group and Ann Davis
responded. Here’s her answer:
“Are you reffering to the Silica Potters sand? It is available from
all Pottery Supplies. It must be pure sand with no chemicals like
iron in it…it supports, fills up hollows and highfire- silica
melts at over 3000’ And it’s a sand, not an inhalent like
alumina…I have been using it for 10 years–the same pile as a
matter of fact–and I never have collapses or drupes— I filled my
puff hearts with it and got…puff hearts”
Elaine, thanks for the heads-up on wholelottawhimsy.com. I’m
familiar with them but I wasn’t aware that they sold vermiculite.
I’ll check that out. And I thought about perlite, too, since it’s
already been exposed to high temps to expand it. But I had never
heard of anyone using it in the kiln, and wasn’t sure why.
Noel, I am curious about the use of silica sand in the kiln. What is
the highest temperature it can withstand without melting? Somewhere
in the back of my mind, there is a vague ‘silica sand=glass’
reference and I know that some jewelry artists slump (melt) glass in
their kilns to create dichroic cabs, so I’m wondering about using it
at PMC firing temps of 1200 - 1650 degrees.
And, Thomas, you said that you considered silica a bad alternative
choice. Can you elaborate on that?
Sounds like a great idea. I had a 5# bag of Alumina Hydrate and
disposed of it - I had used some and didn’t like the dust it created.
Vermiculite is attainable in the Garden Shop - a big bag lasts a long
time. I use that and a “Fire Blanket” that I got from Whole Lot of
Whimsy - it really supports things nicely and isn’t consumed by up to
1650 degrees.
Once I had a request from some ladies making creches and wanted the
fired Vermicuite - it turned to nice brown colors - to use in the
base platform. In this world can recycle almost everything!
Potters use it for coating kiln batts to stop running glaze sticking
pots to them (shelves). It is normally a mixture of alumium oxide,
hydroxide and kaolin. Silica is NOT suitable as an alternative at it
can react with the elements in the furnace and will react with any
glass or flux around and form its own corrosive products (as well as
do you harm). Alternative choices would be Woolastonite, Magnesium
oxide or Magalox. MgO reacts with water when heated but will
restabilize when you heat it beyond a few hundred degrees. Ask for
Batt wash and a ceramics supplier will know what you want. I hope
that this is helpful info for you
Once I had a request from some ladies making creches and wanted
the fired Vermicuite - it turned to nice brown colors - to use in
the base platform. In this world can recycle almost everything!
I don’t know about vermiculite, but you can use the same silica sand
essentially forever, though PMC stains it brown.
Someone said using silica sand is a bad idea but didn’t elaborate.
In my experience, it seems about as inert and benign as anything
could be, so what is the issue, please?
I was on a hunt for vermiculite last year. I searched on Google
because no local garden centers had it. I found it at last in bulk
at a farm and feed store! I guess farmers use it, not sure why.
(Possibly for starting seedlings)
I think perlite is some form of Styrofoam (?) which is why it is used
in potting soil mixes to help retain water. Maybe I’m wrong: but
check that out before trying it. I have some of that too (for rooting
plant cuttings) and it is so lightweight it flies away with the
slightest breeze, unless it is wet. Also a static charge issue:
attracted to everything. Don’t think you could use it, even if it’s
not styrofoam.
Ask for Batt wash and a ceramics supplier will know what you want.
Well, if you ask for kiln wash, they will, but kiln wash is not
suitable, really, because it is very finely powdered. A bat (batt)
is a surface for working or drying clay…
Can you give a reference for silica sand being reactive?
Here is a material data safety sheet for alumina hydrate, It seems
it is in everything from ink to cosmetics as a filler or extender or
pigment. And ranks pretty low of the hazard scale. Also almost any
good sized pottery store should have it. or it can be found on line
from 1 pound and up.
The various forms of silica sand can have differing melting temps
for the component items making it up. Some will melt and stick to
the things in the kiln. Including the heating elements. Possibly
causing problems in the future heating cycles of the kiln, causing a
burn out at that site of clumping or sticking and melting.
The reactivity may not be of a chemical nature that you might be
thinking of. But a physical one.
After 33 years in the public education field and being called to the
art rooms to remove/repair or save the brick work, heating elements
in their kilns. I have seen a lot of stuff that was added to the mix
in the name of art. Whether it was trying for a texture on the
outside or using it inside to prevent the afore mentioned slumping.
Some people are art teachers and some are just teachers in the art
dept. You can run a search for silicosis on the archive during the
last year it has come up a number of times in regards tosand or
media blasting. Or on the net, silicosis, sand box cough,miners cough
etc.
They really don’t have a perfect answer as to the amount or duration
of exposure to the silica dust that causes harm. Almost every study
wants to be boss. So keeping all exposure to a minimum would be
best. Most of the play sand isn’t pure silica sand any longer.
Blasting sand is pure silica and when used outside people in the
work area are using positive displacement masks.
On the subject of masks of the disposalable type. If you are using
them for a hazardous material. When you get done, throw the mask
out. Taking the mask off and hanging it up or placing it on the
bench will only transfer the material inside the mask closest to
your face for the next time.
Hope this covers some of the possible answers to your question
glen
If you allow silica to come into contact with your kiln elements it
fuses and makes hot spots which not only burn out the elements but
also causes the silica to react with the fire clay bricks causing
their melting to a glass which will eat its way through the
surrounding refactory. You get a similar effect from fingerprints on
500w tungsten lamp tubes which are silica. The salt in the
fingerprint creates a hot spot and the silica reacts and forms a
glass which then melts. I have several pieces of kanthal and SiC
with quartz crystals growing on them from contact with silica sand
and many pieces of kaowool and the like with silica that has corroded
its way through it. You only need to get it to melting point once and
then the new compounds will melt at a lower temp and so it
continues. In the UK the kiln shelves are known as batts or bats so
perhaps it is used as a generic term for a flat surface.