|Monthly Tech-Tip |
Alternate Names: Lith Carb, Li2CO3
Lithium Carbonate is the best source of lithium oxide for glazes. It is slightly soluble and a powerful melter. It is unusual to see more than 5% lithium carbonate in glaze recipes.
There are certain basic properties of lithium which are of interest in ceramics. Since lithium has a very small ionic radius in comparison to the other alkali metals, it has a higher field strength. Low expansion coefficients are generally imparted to ceramic compositions containing lithia (beneficial to glazes that tend to craze but harmful to ones already tending to shiver). Lithium carbonate is a very strong flux (also true of lithium fluoride). Because it is such an active melter lithium is valuable in the production of reactive glazes. In contrast, other lithium compounds may be quite refractory: lithium zirconate and lithium aluminum spinel are examples.
There is comparatively little published information on the use of lithia compounds in ceramics. Laboratory investigations indicate that small additions of lithium will react with quartz during firing and eliminate the alpha-beta quartz transition in the cooling cycle. Lithia imparts low thermal expansion coefficients to glasses and also promotes devitrification in glass systems. Smaller amounts act to smooth the glass surface.
Lithium exhibits many properties that are similar to the more common alkali metals sodium and potassium. In many respects is also shows similarities to the elements of the alkaline earth group, especially magnesium.
In addition to being soluble, lithium carbonate produces gases as it decomposes and these can cause pinholes or blisters in glazes. There are insoluble lithium frits available (e.g. Fusion F-493 has 11%) and incorporating one of them to source the Li2O instead is a classic application of glaze chemistry calculations (however for glazes with very high amounts of lithium, like 10%+, it will be difficult to source the Li2O using a frit because significant amounts will be required and this will likely oversupply the other oxides the frit brings). The resultant glaze will be more fusible and will have better clarity and fewer defects.
Lithium carbonate is the best source of Li2O for frits (but obviously the most expensive one). Lithium sources are becoming so expensive that companies and discontinuing products using them. Lithium carbonate powders can be very fine and somewhat grainy. The finer particles powders can deflocculate a glaze slurry, reducing the amount of water required (but also changing other rheological properties).
If you need to substitute this material in glazes and need help, just purchase a group account at Insight-live.com and we can work together to get it done (sourcing the Li2O from a frit or spodumene). We will make a step-by-step video of the initial calculation and then work together in your account to track trials, adjustments and retrials. You will end up with a glaze having better slurry properties, fewer bubbles and better fit.
Lithium carbonate is now ultra-expensive. Yet the reactive glaze on the left needs it. Spodumene has a high enough Li2O concentration to be a possible source here. It also has a complex chemistry, but the other oxides it contains are those common to glazes anyway. Using my account at insight-live.com, I did the calculations and got a pretty good match in the formulas (lower section in the green boxes). Then I made 10-gram balls and did a GLFL test at 2200F (notice the long crystals in the glass pools below the runways). Not surprisingly, this recipe is very runny, that's why the tiny yellow crystals grow during cooling. The new version fires very similar, perhaps better. Our calculated cost in 2022 was $17.84 vs. $10.40 per kg. But there is a practical cost: Poor slurry properties. The spodumene sources so much Al2O3 that 70% Alberta Slip had to be dropped to accommodate it! How does one use this type of glaze without ruining kiln shelves? Using a catcher glaze is one answer.
These materials have many issues. They can create problems in glaze slurries (like precipitates, higher drying shrinkage), cause issues with laydown density and produce fired surface defects (like pinholes, blisters, orange peeling, crystallization). Lithium and barium carbonates have toxicity issues and the carbon burns off during firing (with lithium, for example, 60% of its weight is lost). Yet the oxides that these materials supply to the glaze melt - ZnO, Li2O, BaO and SrO can be sourced from frits (removing most of the problems and imparting better glaze melting). Fusion Frit F-493 has 11% LI2O, F-403 has 35% BaO, F-581 has 39% SrO and FZ-16 has 15% ZnO. Of course, these frits source other oxides (but such are common in most glazes). Using glaze calculation you can often duplicate the chemistry of glazes while sourcing these oxides from frits. This being said, using the frits is about achieving a quality and avoid defects over concerns about their extra cost. Often the benefits lower the overall cost of production.
This is 85% Alberta Slip, 11% lithium and 4% tin fired at cone 6 in oxidation. Like the original Albany version, it has a very low thermal expansion (because of the high lithium content) and likes to shiver on many bodies.
Left is G3933G1, an Alberta Slip based glaze. Right is Amaco PC-32, Albany Slip Brown. The difference is that they are adding lithium carbonate to supercharge the melting of this type of glaze, which makes it reactive - where thick in the recesses it crystallizes to a much lighter color. Where thin it amplifies the brown body color. The use of the lithium explains why this particular product is more expensive ($2 at time of writing). At current lithium carbonate costs that would cover 6-8% they are adding.
Lithium is getting really expensive. These are four recipes submitted by a customer who wonders if there is a substitute. The answer is not simple, each glaze is a unique situation. Fortunately, lithium carbonate is almost always a minor addition (in the first two recipes it is 1% and 3%). Lithium is a powerful low expansion flux, in some cases, a low melting low expansion frit could perform the same function (e.g. Ferro 3249). Even for the 6.5%, as in the third one, this could still work. But in these cases wouldn't it be better to continue using lithium? Even for the last one that has 9%? It's only expensive if you make glazes and don't use them. Perhaps a solution is to make them as brushing glazes, a 1-pint jar only needs about 350g of powder (that is only about 30g for recipe 4).
This situation can also be considered as an opportunity to rationalize the recipes you use. Let's pretend that each of these might be used on functional ware and should measure up to common sense recipe limits. The Gerstley Borate in three of these is also a red flag, that won't be available shortly (calculating how to source B2O3 from frits is better anyway). During that process, you might find that lithium is not even needed. Another issue is thermal expansion. Notice that one of these calculates to 8.5 and another to 9.6! Those are virtually certain to craze. Why not lower that number while removing the Gerstley Borate? Notice that two of these have clay percentages over 70% (Alberta Slip and Gerstley Borate), these are virtually certain to crack on drying (and crawl on firing), that can also be fixed. The percentage of titanium, Zircopax and rutile in the fourth one are guaranteed to make it crystallize heavily on cooling produce big problems with cutlery marking and staining.
It is fabulously expensive now, so obviously we have to be sure the material from a new manufacturer is the same. We found a wonky glaze having 6% of it (lithium is a very powerful flux so small percentages are normal). By 'wonky' I mean one that gives little priority to function - it runs, crystallizes and crazes like mad and fires very differently depending on temperature, clay and firing schedule. We glazed a variety of pieces using this recipe and found it to work equally crazily on them all! These two, the original lithium on the right and the new one on the left, looked the most interesting, likely because of being on a dark clay body. Obviously, this type of recipe is very sensitive to thickness, we attributed the difference here to that.
Fusion Frit F-493
This frit is very valuable for one simple reason: It is a higher-quality source of Li2O for glazes than raw lithium carbonate. It contains 11% Li2O.
Spodumene is a lithium sourcing feldspar, an alternative to lithium carbonate to supply Li2O to ceramic glazes. Contains up to about 8% Li2O.
Lithium Carbonate (Foote)
Replace Lithium Carbonate With Lithium Frit Using Insight-Live
Raw lithium carbonate can often be replaced with a lithium-containing frit if you can do the chemistry. And you can at insight-live.com.
Lithium Carbonate at wikipedia.com
Materials that source Na2O, K2O, Li2O, CaO, MgO and other fluxes but are not feldspars or frits. Remember that materials can be flux sources but also perform many other roles. For example, talc is a flux in high temperature glazes, but a matting agent in low temperatures ones. It can also be a flux, a filler and an expansion increaser in bodies.
Generic materials are those with no brand name. Normally they are theoretical, the chemistry portrays what a specimen would be if it had no contamination. Generic materials are helpful in educational situations where students need to study material theory (later they graduate to dealing with real world materials). They are also helpful where the chemistry of an actual material is not known. Often the accuracy of calculations is sufficient using generic materials.
Lithium Carbonate Toxicity
|Oxides||Li2O - Lithium Oxide, Lithia|
|Solubility||1.3 g/100ml at 20 deg C|
|By Tony Hansen|
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