On the right is L213, a body made using Texas talc and Kentucky ball clay. On the left is L3778H, a translucent cone 6 porcelain made using Grolleg kaolin, Nepheline syenite and silica. These test tiles were in the same cone 04 firing. Since both of these bodies have similar porosities and fired strengths at cone 04, does that mean one could use the porcelain? It appears the answer is yes. Why is that again? Because low-temperature artware clay doesn’t need vitrification; all the bodies are porous.

What could make this work? This crystal clear glaze, G1916QL1, fits the L213 but crazes after a few days on the porcelain. Increasing the firing temperature to cone 03 extends that time to 3 weeks. Cone 02 would likely extend it further. Adjustments to the glaze recipe (e.g. 400 mesh silica and increasing its percentage) would lower the thermal expansion and improve fit even more. This whole scenario is doable for DIY potters who mix their own bodies and glazes, especially for casting. The materials to make the porcelain are kaolin, silica and feldspar, even inexpensive kaolins would produce a body almost as white as this one at low fire.

Industrial spodumene is found in massive quantities across major mining regions like Australia, Africa, and North America. Yet if this 1.5kg rock was pure spodumene, it could be ground and sold for $45 (prices at ceramic suppliers in UK, US and Australia are about $31-35/kg in June 2026). The actual mining commodity price is US$2,100/tonne, pricing this rock at $3. That means finely ground ceramic spodumene is currently selling for 10+ times the mine/concentrate price. The battery industry is responsible; it has effectively repriced a ceramic feldspathic mineral as "lithium ore"!

What about lithium carbonate? Albemarle reported an average industrial price of US$19.53/kg in Q2 2026. So potters currently pay only up to 8 times that! Yet, the processing is formidable: The ore must be crushed and beneficiated, then subjected to a high-temperature calcination that converts alpha spodumene to the more reactive beta form, followed by acid roasting, leaching, neutralization, impurity removal and further conversion.

Fortunately, in ceramics, a kiln doesn't care what the source of Li2O is; there are advantages to sourcing it from spodumene and from the carbonate.

This social media post is a little shocking: tin oxide at 1/5th the cost! I assume it is cheaper there because South American consumers are much closer to the tin-production and industrial-chemical supply chain. In North America, a potter is often buying a specialty imported ceramic material that has passed from the mine to the smelter/refinery, then the chemical manufacturer, then the importer, then the ceramic-material wholesaler, then the pottery supplier who repackages it into small sizes, documents it with an SDS and carries it on slow-moving inventory. Those services are legitimate costs, but they can dwarf the actual processing cost of converting tin into tin oxide. That being said, other materials share similar costs, why are they so much less expensive?

I am looking to match the reduction-fired dolomite matte mug on the right, but in cone 6 oxidation. I must duplicate the glaze color and surface character. But more difficult is the speckle size, color, density and edge bleeding. The speckle is the biggest challenge, but I met that by making my own by mixing the body and G2926B glossy glaze 50:50 and adding 10% black stain. Then I slurry it, dry it, fire it in a crucible (which I make from L4404A with an L3693E liner), crush it by hand using my shusher and screen it. I am using G2934 cone 6 magnesia matte as the glaze on this mug on the left. I add 0.5% minus 20 mesh speck to achieve this result. The next step in this project is to sieve out the smallest specks, switch to the G2934 matte glaze in the speckle recipe (the specks are too shiny here), and switch to dark brown stain instead of black. I will also need to control the degree to which the specks bleed at their edges (by adjusting the glaze:body ratio) and tune the degree of matteness (by adjusting cooling speed of the kiln). A small amount of green or blue stain is also needed to match the glaze color. There is no question that an authentic reproduction is possible; methodical testing with good records is the key to accomplishing that.

Typical pottery porcelains are variations on the traditional triaxial body and commonly contain around 50% clay, either kaolin, ball clay or a mixture. Since the clay fraction is normally the largest source of iron and titanium impurities, its purity has a major influence on fired whiteness—especially in reduction.

These mugs were fired in the same kiln load at cone 10R and have the same clear glaze, G1947U. The mug on the left is a Grolleg kaolin porcelain (50% Grolleg kaolin, 25% silica and 20% Mahavir feldspar, 5% bentonite). The one on the right is 15% M23 ball clay, 40% #6 Tile kaolin, 15% Nepheline, 25% silica, 3% bentonite. The grey is the cumulative effect of the impurities in these clays.

Grolleg is considerably more expensive, but this is one place where the extra purity is plainly visible. Want to push whiteness even further? Use an ultra-low-iron New Zealand kaolin and replace ordinary bentonite with Veegum or another clean-burning plasticizer.

Until now, I thought magnesia matte glazes need high Al2O3 and a low Si:Al ratio. But this melt flow test suggests otherwise. The cone 6 glaze on the left (A) is close to my usual target of 0.4 MgO, 0.1 B2O3 and a ratio of 6:1 (approaching ceramic tile proportions). It is thus a classic high-MgO / higher-Al2O3 magnesia matte. The melt's high viscosity, limited flow, and phase separation produce the very fine surface texture.

However, glaze B has a super-high Si:Al ratio of 14:1. Yet it is not running much more and is almost as matte. How? It seems I shifted the matteness mechanism. Cutting the Al2​O3​ in half and spiking the SiO2​ has moved from a high-alumina magnesia matte toward a low-alumina, high-silica calcium/magnesium silicate matte. The massive surplus of SiO2 coupled with oversupplied MgO and plentiful CaO has weakened the "glue" that keeps the latter busy in the glass matrix, so they precipitate out (as calcium-magnesium silicates, diopside CaMgSi2​O6​ or enstatite MgSiO3, according to Google). This still creates a matte surface by crystallization and phase separation. The degree of matteness could likely be enhanced by slow cooling. And possibly 400 mesh silica.

This is L4588 red burning porcelain. I got the idea after coffee break and was rolling and pressing specimens right after lunch. How?

The major reason is not being intimidated by mixing body and glaze tests. Another is having all the tools and materials close at hand (shown here). Third is a good record-keeping system where I make sure to enter results, notes, pictures and links to related tests at every stage of a project.

• 10.30 am: Got the idea to make this, created a record in my Insight-live account, code-numbered it and printed the recipe.
• 10.35 am: Started weighing it out.
• 10.40 am: Blender-mixed it really well to remove all agglomerates.
• 10.45 am: Poured it onto my plaster bat.
• 12.30 pm: It had stiffened to the perfect consistency to roll a couple of SHAB test bars and press and stamp some porcelain theme-rocks.
• Next day: In a cone 6 kiln load.
• Next day: Incredible red porcelain.
• Following weeks: Study the results and decide what recipe changes would improve it for round 2.

This body is 70:30 kaolin:feldspar (fired at cone 6 with glaze G2926B). The fired body has a vitreous porcelain-like surface. But, this dense craze pattern indicates a very serious fit problem. The COE (thermal expansion) of this body is much too low. There isn't a glaze-fix solution to this. Reformulating it enough to fit, while maintaining the firing characteristics, would be well beyond the expertise, material availability and budget of any typical pottery or manufacturer. All that work would just boil down to "compensating for an unusually low-expansion body". Adding quartz to the body to raise its COE is the appropriate conventional solution. An initial test would be to substitute 25 of the kaolin for 200 mesh silica. It is refractory, and while the finer particles will be dissolved by the feldspar, enough of the larger pure quartz ones will remain to impose their very high COE on the fired matrix.

The other issue is with the flat particle shape of kaolin. The throwing process has lined up the predominant kaolin particles concentric to the centre. During drying, and especially firing, more shrinkage occurs across them than along them. All ten of the cups, which I made and dried in my normal, careful fashion, cracked like this! The solution is adding a filler, one with non-platy particles. Silica is perfect; the grains act like aggregate in concrete, strengthening the matrix and separating the clay particles, forcing them to orient more randomly.

In order to add 0.5% of CMC gum to this glaze I need to calculate the water content to know how much powder is present. Other scenarios for this are adding Frit 3135 to cone6ify a cone 10 glaze, adding stain to color it, adding zircon to opacify it.

I put a teaspoon of the glaze (well stirred) on the tared tray. It weighed 5.04g (this 0.01g scale is accurate to 1/100th of a gram). WhenI dried the tray under a heat lamp, it weighed 2.46g. The water content of the slurry is thus (5.04 - 2.46) / 5.04 * 100 = 51.2% (the solids content is thus 48.8%). To blender mix 0.5% CMC gum into this I weighed the jar with glaze at 680g and the jar itself at 35g. Thus 680 - 35 = 645. 48.8% of 645 is 315g of powder. 0.5% of 315 is 315 * .005 = 1.6g of CMC gum.

The ceramic materials we depend on are no longer commodities we can assume will always be cheap and available. Lithium materials can suddenly multiply in price. Cobalt colorants can double. A familiar plaster can disappear. Zircon and stains can jump with global mineral markets. Products made from these (e.g. glazes, underglazes) follow suit. And freight can make even inexpensive clay expensive.

The answer is not to stockpile everything—it is to learn how to adapt. A potter who tests, documents and understands materials can reduce cobalt, replace lithium, qualify a new plaster, reformulate around a discontinued feldspar, make better use of a local clay, and even make his/her own glaze and underglaze. Accumulated knowledge from ongoing testing becomes insulation against both inflation and disruption. Think of your test records as a savings account. Every melt test, firing schedule, recipe adjustment, clay test and photograph is a small deposit. When supply problems or price increases arrive, years of organized observations suddenly become very valuable, giving your choices and options others don't have.