Potters & Sculptors - Making Rock from Mud
How much to stock is a question that has to be considered and balanced by variables such as: your production output, studio space available, glazing techniques (smaller batches for spraying, larger batches for dipping), mixing a few stock glazes, or continuously testing and using a wide variety of glazes, price break points and percentages.
My glaze material space is limited to about 10 feet along one wall of my basement.
I buy 50# bags of clays, feldspars, silica, and my most often used frits. Other materials I purchase in quantities that I think will last me for a year, or the largest amount I can comfortably afford. Some things I only stock in 1 or 5 lb amounts to use in test batches or the powerful, expensive colorants and stains.
This was my glaze materials inventory at the beginning of the year. At the quantities I purchased, the inventory had a value of just under $900. I find that it is sufficient to mix a majority of the glaze recipes I'm interested in testing, and with reasonable substitutions I can test even more. I can usually mix a 1,000 gram batch of a new glaze with materials on hand and reorder to cover diminishing stock.
|Item||Gram Amount||Pound or Unit Amount|
|Aluminium Oxide (calcined)||2390||5.00|
|Ball Clay, Kentucky OM4||31.60|
|Feldspar, G200 (old formula)||8.00|
|Iron Oxide (Yellow)||2160||4.76|
|Iron Oxide (black)||616||1.36|
|Iron Oxide (old red)||400||0.88|
|Iron Oxide (special red)||2303||5.07|
|Iron Oxide (high purity red from US Pigment)||2342||5.16|
|Stain, Mason 6004 red||473||1.04|
|Stain, Cerdic red 279497||192||0.42|
|Stain, Spectrum red 2084||114||0.25|
|Stain, Mason Pras. Yelo 6450||114||0.25|
|Stain, Mason black 6600||454||1.00|
|Stain, Mason Yelo 6406||454||1.00|
|Stain, Mason Yelo 6485||454||1.00|
|Tile Clay (No. 6)||2223||4.90|
It is wise to buy the largest quantities you can afford and have storage space for. This reduces changing batch characteristics, and the possible labeling and contamination mistakes arising from your ceramic supplier breaking down full bags into smaller quantities.
I find life easier keeping all of the glaze material with free silica segregated onto a couple of pallets covered with tarps requiring a respirator to access - silica, talc, bentonite, some feldspars and even kaolins if you're really particular. Being outdoors makes it easy to control the dust around these pallets with a hose. The danger is the airborne silica you can't see.
This lets us access the majority of our glaze materials without a respirator.
As you've discovered, most glaze materials are surprisingly economical, ranging from $10 to $30 for each fifty pound bag, with significant volume discounts for whole bags reducing the price by 50% to 90%. Fifty pound bags of glaze material start to get a little more expensive around spodumene, strontium carbonate, manganese dioxide (due to the popularity of gold glaze) and spanish iron oxide at $45, with man-made frits ranging up to $100 for a fifty pound bag.
The only large volume items topping $100 for a fifty pound bag are magnesium carbonate $160, bone ash $201, and Ferro Frit 3249 containing magnesium at $212. Laguna Clay delivers all of these bags along with our clay in Los Angeles for one flat $30 delivery fee.
The remainder of glaze ingredients have minimal volume discounts and are more expensive so we buy in smaller ten pound or one pound quantities: rutile; zinc oxide; titanium; imported specialty supplies; lithium carbonate or lithium fluoride; tin oxide; colorant oxides and mason stains.
The result is most glazes cost $0.30 to $0.75 a pound, plus the cost of colorants - which range from nothing for a clear up to the overwhelming majority of the glaze cost.
This is 2/3 less costly than a dry mix and 80% or 90% less than a pint of prepared glaze.
A relatively costly example is our Cream Breaking Rust recipe which costs $0.67 per pound for the base glaze with $3.36 of colorant oxides for a total of $4.03 per pound.
$4.03 100.0% Cream Breaking Rust ^5 to 8
$0.40 30.7% Ferro Frit 3134
$0.09 26.6% Custer Feldspar
$0.05 18.1% Silica
$0.04 10.6% Wollastonite
$0.03 8.4% Kaolin
$0.05 3.3% Strontium Carbonate
$0.01 2.3% Talc
$3.11 13.0% Tin Oxide
$0.25 6.0% Red Iron Oxide
For comparison, the most costly glaze in "Mastering Cone 6 Glazes" using 50 pound bag pricing is $1.46 per pound for Variegated Slate Blue, using cobalt, copper and rutile. Only their Raspberry recipe is more costly at $2.07 a pound due to the 7.5% tin oxide used. . . . But I do like tin.
Cream Breaking Rust with 13% Tin Oxide
In total our glaze material fills seven large pallets, so you do need some place to put it all.
You need to locate the largest volume supplier of ceramic supplies in your local area.
We're fortunate in being located within 35 miles of Laguna Clay in the City of Industry so truck delivery is $30 when we order 1,000 pounds or more of clay or related material. Their Axner subsidiary in Orlando Florida charges more for a 2,000 pound minimum when delivering to Miami.
A 50 pound bag of Silica can cost as little as $5, but it will cost $50 to ship one bag via UPS Ground.
This is why Laguna has three lists of clay: Western; Northeastern; and Southeastern. If we actually wanted a clay made by Laguna Clay in Florida or Ohio there's a higher cost, but it can be far cheaper than shipping from their eastern factory by UPS, because Laguna ships train car loads, and has a steady stream of the largest trucks I've ever seen, but it does cost more.
Here's the distribution network for Laguna. http://www.lagunaclay.com/distributors/
There are also wholesale suppliers like Hammill & Gillespie which distribute a selection of mined products, like Spanish Iron Oxide from Prominfer in Spain. It could be possible some of these supplies are cheaper in your area from a Hammill & Gillespie than from a Laguna, but they may have purchase minimums.
Laguna doesn't sell Bayferrox synthetic iron oxide so I get to pay for UPS shipping from Pittsburgh from the cheapest supplier I could find - one who in turn sells Bayferrox to many other ceramic retailers.
One other example, Custer Feldspar is mined in Custer South Dakota. At retail, one ton of Custer Feldspar, a pallet of 40 fifty-pound bags, costs $0.23 per pound in Chicago at Great Lakes Clay or $0.35 per pound for one bag. This fifty-pound bag which costs $17.50 in Chicago costs us $20.50, 17% more at Laguna. But Laguna's prices are far lower on items mined in or near California.
Clearly shipping is a significant cost, but when shipped in volume it's not as significant as the volume discount offered on that product.
I am so excited to learn how to mix glazes for dipping. Your chart of chemicals with suggested amounts is a huge help. Are you aware of any cd's on the market that will take me from start to finish on the entire process and logic of mixing the glazes? Thanks.
I think most people begin as I did with a book like "Mastering Cone 6 Glazes". The glazes in that book are easily the least expensive glazes we've ever made at our studio, and it explains the concept behind making glazes.
I found the DigitalFire Materials Database around the same time, and with a chemistry background it was invaluable. This listing is for Ferro Frit 3134 which makes a great clear glaze when combined with Kaolin to provide the missing alumina.
The only advice that wasn't in that book is buying a container of Calcium Chloride. A small sprinkle of these white pellets will suspend the clay in any glaze, far better than epsom salts or acids. It's sold as a compound to melt ice on sidewalks, which means in Los Angeles we had to buy Calcium Chloride on Amazon.com because locally ice is only available in beverages.
The two ingredients which contain a lot of free silica, which causes silicosis when breathed in, is not surprisingly Silica, Talc, which is silica and magnesium, and Bentonite. A respirator is a really good idea when using these two materials. We keep them outdoors. Feldspars, Kaolins and Clays have much lower levels of free silica, where a respirator is probably a good idea but I don't insist on it.
The ugly truth behind making your own glazes - more than six pallets worth.
Behind an Optometrists office.
Covered by tarps, with custom cone 6 tarp weights tied on each corner.
High-silica pallet with silica, talc and kaolins. The Feldspar pallet also contains some free silica.
The clay locker a converted metal garbage skip.
Materials in use. Easy to access but not scenic.
Frits under a long dead slab roller
More expensive oxides and other material in the plastic garden cabinet (wood reinforced).
A pastoral setting with blackberries, tomato and asparagus plants behind the photographer, along with a fig and pomegranate trees.
A good resource George.I priced the list by australian suppliers and came to apprx $1500 (Say $us 1500)
I am dubious of a few items which are listed as toxic or not recommended for potters studios by
either Hesselberth and Roy, Mastering cone 6 glazes, p132 or Richard Zakin, Electric kiln ceramics 3rd Edition, p288. These include Barium carbonate, chrome oxide, and Lithium carbonate. I am no expert but reading the Digital fire database further muddied my understanding. Cheers
I think the most dangerous raw materials in a ceramic studio are Silica/Flint and Talc.
(also bentonite and some feldspars).
We all know these raw materials have very high levels of free silica which waft into the air and remain there after being disturbed. Respiratory exposure to silica is cumulative.
I may be wearing a respirator when I add flint or talc to a glaze recipe, and I hold it less just a few centimeters above the bottom of the container I'm adding it to, but there is still some free silica added to the air. The most dangerous part of the silica plume is the part we can't see because those are the particles which get trapped deep inside your lungs. And you take away free silica on your clothes, even after you wash your hands before removing the respirator.
Compare the clear hazard of free silica to other raw materials.
Chrome Oxide is a respiratory hazard, as are Manganese Dioxide, Cobalt Oxide or Carbonate, and Copper Oxide or Carbonate and Iron Oxide - but none of these items waft into the air and remain there like free silica does as they're very dense. All of these items are toxic if eaten (the iron is safe but not the contaminants in the iron oxide) and nano-particles of colorants can be absorbed through the skin in small quantity. Both chrome and manganese fumes from the kiln are a health hazard, and you can develop contact dermatitis to most colorant oxides after chronic exposure.
We should avoid eating Lithium Carbonate and Spodumene, and there is some leeching concern in a glaze. But Lithium Carbonate is used as a medication at levels thousands of times higher than any glaze could possibly leech.
I don't like to use Lithium Carbonate is because 29% of it doesn't get through our sieve. Even the finest grades leave 17% on a 100 mesh sieve. This is not a problem with Lithium Fluoride and is a much smaller problem with Spodumene.
Lithium Fluoride is a superior flux, will not decompose into Lithium and Fluorine at kiln temperatures, and its lithium isn't available to leech from a glaze. Lithium Fluoride does cost twice as much as Lithium Carbonate, but it has no problem being sieved.
Barium Carbonate is a deadly poison if you eat it. In the stomach mixed with acid, it becomes Barium Chloride which is readily absorbed, unlike Barium Sulfate which you drink before taking some x-ray tests. Barium Carbonate is used as a rat poison, so using barium carbonate in place of wheat flour in foods causes a very high mortality rate.
You may not think you're using Barium . . .
. . . but it is added to prepared clays, slips, some iron oxides, and many prepared glazes. Barium Carbonate or Barium Hydroxide/Barium Oxide is added to combine with free salts forming insoluble compounds which prevents scumming in fired clay and glazes. Reading the MSDS (Manufacturers Safety Disclosure Sheet) will tip you off to these inclusions.
We had mice at our outdoor studio so I left out clumps of barium carbonate cheese and barium carbonate peanut butter for them. They kept eating these 50% barium carbonate treats for weeks before they died dehydrated or moved elsewhere in search of water. Larger mice may require such a large cumulative dose over time that you wonder it barium is actually toxic. As with lead, barium toxicity is cumulative so we don't let people use barium or leaded glazes on functional ware, but as a mouse or rat poison it leaves a lot to be desired.
We also have metal saturation glazes labelled as unsafe for food use, including manganese gold and metallic glazes and nickel and copper saturation glazes. But most of these colorants add a bitter taste to food if the colorant leeches into the food or drink, which is one reason why barium (tasteless) and lead (sweet or tasteless) are especially dangerous.