Make frit melt fluidity test balls using CMC gum as a binder

Traditionally we have made GBMF test balls of non-plastic materials (e.g. frit) using Veegum as the binder. However, Veegum interacts with materials enough to affect melting. CMC gum is better. I use 10g frit (the right amount for one ball), 0.1g CMC (1%) and ~3g of water. Of course, you need a scale accurate to 0.01g to be able to weigh out only 0.1g (otherwise consider doing 50g). The procedure that seems to work best is to shake the frit/CMC mix in a small bag, pour it into a bowl, pour in a tiny amount of water and stir and smear with a spoon. With the right amount of work and water the thickened material will become cohesive and can be formed by hand. Does cornstarch work? No, it does not gel like this and the mix is not plastic either. Psyllium? Yes, but it has a flakey texture and demands more water. For better formability use 1.5% CMC gum - however, the ball will dry slower and much harder. Other powders will behave differently (needing more or less water, forming better or poorer, dewatering slower or faster). You will need a plaster surface to absorb the excess water (which invariably happens).

Related Pictures

VeeGum can plastify frits for making melt-flow test balls

Frit and veegum powder ready to mix with water

Nothing compares the fired properties of frits as well as a melt-flow comparison. Remarkably, each frit has such a unique melting behaviour that it is possible to identify them and determine if two are similar (without knowing the chemistry). But frits need a binder to make them plastic-formable. I mix 50g of frit with 1.5g of VeeGum (or 100g/3g) then stir the powder into 40g of water in a cup. That produces a consistency that is easy to stir smooth (using a teaspoon) but is still fluid enough to level out on a plaster bat (for dewatering to plastic consistency). The 3% VeeGum is not enough to affect the melting behaviour, but it makes them pretty workable (however each frit does exhibit different tactile characteristics). I roll them into 12g (wet) balls, then dry them. They fit nicely into the reservoir for my GBMF test.

Preparing balls for a melt fluidity firing test

Here is how to prepare a melt-flow ball for the GBMF test or the GLFL test: Weigh 11g of the frit and 0.33 of Veegum (the latter plasticizes the frit and imparts dry hardness). Put them in a small ziplock bag. Zip it to entrap air, roll the zipper down to inflate it and shake well to mix the Veegum and frit. Stir the powder into plenty of water in a small bowl. A brush works best for quick delumping and cleaning out the bowl when pouring onto a plaster slab. It dewaters very quickly, after about 10 seconds, just as the water sheen is gone, peel it up with a rubber rib. Smear it back down and peel it up every few seconds until it is plastic and formable (not sticky). Roll it into a ball, label it and dry it under a heat lamp (could take an hour, the Veegum really holds on to the water). When dry use a sharp knife to cut off enough to bring it down to 10 grams. One caveat: The Veegum is a melting catalyst, when comparing melts both sample should contain the same percentage.

Links

Tests	Glaze Melt Fluidity - Ball Test A test where a 10-gram ball of dried glaze is fired on a porcelain tile to study its melt flow, surface character, bubble retention and surface tension.
Glossary	Ceramic Binder Binders are glues that harden ceramic powders as they dry. They enable improved surface adherence. And slower drying.
Materials	CMC Gum CMC gum is indispensable for many types of ceramic glazes. It is a glue and is mainly used to slow drying and improve adhesion and dry hardness.

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