Glazes must be completely melted to be functional, hard and strong. Many are not. This compares two glazes to make the difference clear.
The picture below is a flow tester that was fired at cone 6. The tester itself is Plainsman M370. The glaze on the right is G1214W, a typical cone 6 transparent used by potters. It is fluxed by a boron sourcing frit. The glaze on the left is typical of what many use to achieve a matte. The recipe is:
But this glaze is not flowing at all whereas the boron-fluxed glaze has run right to the bottom (and it is not even considered a highly fluid glaze). This simple comparison teaches us many things about glazes and even ourselves. Here are some of them.
Understanding your glazes is so much better, especially when it comes to dealing with their problems (and this one would have plenty!).
Look at recipes before wasting time and money on them. Are they serious? This is a cone 6 GLFL test to compare melt-flow between a matte recipe, found online at a respected website, and a well-fluxed glossy glaze we use often. Yes, it is matte. But why? Because it is not melted! Matte glazes used on functional surfaces need to melt well, they should flow like a glossy glaze. How does that happen? This recipe has 40% nepheline syenite. Plus lots of dolomite and calcium carbonate. These are powerful fluxes, but at cone 10, not cone 6! To melt a cone 6 glaze boron, zinc or lithia are needed. Boron is by far the most common and best general purpose melter for potters (it comes in frits and gerstley borate, colemanite or ulexite; industry uses more boron, zinc and lithia frits). The lesson: Look at recipes before trying them.
True functional mattes have fluid melts, like glossy glazes. They need this in order to develop a hard, non-scratching durable glass. The mechanism of the matte on the right is high Al2O3 (G1214Z), it is actually melting more than the glossy glaze on the left (G1214W).
Out Bound Links
This device to measure glaze melt fluidity helps you better understand your glazes and materials and solve all sorts of problems.
By understanding how glazes melt and materials and chemistry interplay to determine behavior and temperature of melting and testing degree of melt you control the melting temperature of your glazes.
A glaze that is not glossy. Of course, unmelted glazes will not be glossy, but to be a true matte a glaze must be melted and still not glossy. To be a functional matte it must also resist cultery marking, clean well and not leach into food and drink. Thus it is not easy to make a good matte glaze. I...
In Bound Links
Moving a cone 10 high temperature glaze down to cone 5-6 can require major surgery on the recipe or the transplantation of the color and surface mechanisms into a similar cone 6 base glaze.
The trade is glaze recipes has spawned generations of potters going up blind alleys trying recipes that don't work and living with ones that are much more trouble than they are worth. It is time to leave this behind and take control.
We have included this page to warn you about recipes that you find online. Be careful about wasting your time. And money. Do not think you will find a magic solution to all your dreams! What you will more likely find is alot of frustration and a stock of useless materials. Better to have two recipes...
By Tony Hansen