Matte cone 6 glazes have identical chemistry but one melts more. Why?
These are 10 gram balls that we melted on porcelain tiles at cone 4 (top two) and cone 6 (bottom two). They compare the melt fluidity of G2934 (left) and G2934Y (right). The Y version sources its MgO from frit and talc (rather than dolomite). It is a much more fluid melt because the frit is yielding the oxides more readily. But Y has a key benefit: It has a much lower LOI, producing fewer entrained air bubbles and therefore fewer surface defects. And, even though it runs much more, it has the same matte surface! As long as it is applied at normal thickness, the extra melt fluidity does not cause any running. And it has another benefit: Less cutlery marking issues. It is actually a very durable and practical food surface glaze, having a low thermal expansion that fits almost any body. Although these appear glossy here, on ware they have the identical pleasant silky matte surface.
Context: Ferro Frit 3249, G2934Y - Cone 6 Magnesia Matte Low LOI Version, G2934 - Matte Glaze Base for Cone 6, G2934 vs. G2934Y cone 6 matte glaze, Matte Glaze, Dolomite Matte
Thursday 11th January 2018
Smash your ware to see if it is strong!
I use a nylon hammer, and glasses of course. I just filled two five-gallon pails and three boxes. Every type of clay and glaze I currently use. Every temperature. I started with a commercial Denby stoneware piece to get a feel for how quality ware should break. It becomes immediately evident which pieces are weak by the way they shatter. Breaks with knife-like edges indicate strong body/glaze combos. Strong ware breaks into fewer pieces. Crazed ware is weak. Low fire vitrified ware can be very strong. High-fire ware can be weak (e.g. iron stonewares having high porosities). Give attention to this, make quality ware.
Context: Fired Strength
Saturday 11th November 2017
Why would a low fire transparent require four frits?
To get the needed chemistry to avoid boron blue clouding (calcium borate crystals). The one on the right clouds, the other does not. Why? Differences in the chemistry (as seen in my account at insight-live.com). G2931K, on the left, has greater Al2O3 (which impedes the growth of crystals), lower CaO (starves their growth) and more boron (for better melting). There is actually no practical way to adjust the recipe on the right (by supplying MgO with talc and fiddling with frit percentages) to achieve this. Frit 3124 lacks Na2O and B2O3. 3134 has excessive CaO and almost zero Al2O3. Talc does not melt well enough. But Frit 3249 supplies the needed MgO and has lots of B2O3 and low CaO. And Frit 3110 has low CaO and supplies the needed Na2O.
Context: G2931K - Low Fire Fritted Zero3 Transparent Glaze, G1916M - Low Fire Frit 3134:3124 Glossy Transparent, Boron Blue, Frit, Glaze Chemistry
Thursday 9th November 2017
Match calculated COE to dilatometer-measured body COE? No!
Why? Firing temperature, schedule and atmosphere affect the result. Dilatometers are only useful when manufacturers monitor bodies AND glazes over time and in the same firing conditions. Calculated values for glazes are only relative (not absolute). The best way to fit glazes to your clay bodies is by testing, evaluation, adjustment and retesting. For example, if a glaze crazes, adjust its recipe to bring the expansion down (your account at Insight-live has the tools and guides to do this). Then fire a glazed piece and thermal stress it (300F into ice-water). If it still crazes, move it further. If you have a base glossy glaze that fits (and made of the same materials), try comparing its calculated expansion as a guide. Can you calculate body expansion from oxide chemistry? Definitely not, because bodies do not melt.
Context: IWCT 300F:Ice Water Crazing Test, Calculated Thermal Expansion, Crazing
Monday 23rd October 2017
An incredible silky matte surface supports wild colors at cone 6 oxidation
This is the G2934Y matte base recipe with only 8% Cerdec Orange encapsulated stain. G2934Y employs a frit-source for the MgO (as opposed to G2934 which sources the MgO from dolomite). The orange color is brighter on the mug on the left because the porcelain is whiter, Plainsman Polar Ice (the other one is #6 Tile Kaolin based, P300). If this was a glossy glaze the required percentage of stain would be higher. Other colors, like yellow, are equally vibrant. But not all, testing is needed.
Context: G2934 - Matte Glaze Base for Cone 6, G2934Y - Cone 6 Magnesia Matte Low LOI Version, Concentrate on One Good Glaze, Encapsulated Stains, Matte Glaze, Semi-Matte Glaze
Thursday 19th October 2017
A black engobe transforms the floating blue glaze over it
M340 stoneware fired to cone 6 (drop-and-hold schedule). The L3954B engobe fires deep black (it has 10% Mason 6600 black stain instead of the normal 10% Zircopax). It was applied inside and partway down the outside (a much less messy process than using a black clay body). They were bisque fired and glazed inside using the base GA6A Alberta Slip amber clear (using Frit 3195). The outside glaze is Alberta Slip Rutile Blue (you are seeing it on the bare buff body near the bottoms and over the black clay surface on the uppers). To learn more about how to make the engobe and start making black pots click "Product Data Sheets" at PlainsmanClays.com and go to the section on Medium Temperature.
Context: L3954B - White Cone 6 Engobe for Plainsman M390, M340, Cone 6 Drop-and-Soak Firing Schedule
Monday 2nd October 2017
Dark Umber-Stained Engobes on M340 at cone 6
This is the standard Plainsman L3954D white engobe recipe with the 10% Zircopax switched for Burnt Umber. The result is a dark, rich, ultra-gloss brown (almost black). The engobe is applied inside and half-way down the outside. The mug on the left is glazed inside and out with the base GA6A Alberta Slip cone 6 recipe (but uses Ferro Frit 3195 instead of 3134). The one on the right has the same glaze on the outside but the G2926B clear transparent on the inside (it is micro-bubbling). This engobe works even better with a black stain.
Context: L3954B - White Cone 6 Engobe for Plainsman M390, M340, GA6-A - Alberta Slip Cone 6 Amber Base Glaze
Monday 2nd October 2017
Making ceramic tile shapes by 3D printing your own cookie cutters
This was done on an affordable RepRap printer. The shapes were drawn in Illustrator, extruded in Fusion 360 and sliced and printed using Simplify3D (which took about 30 minutes each). The round wooden block was used to press them into the clay. The plastic wrap made sticking a non issue (and rounds the corners nicely). The clay is a low fire, buff burning talc body (Plainsman L212). Commercial bottled glazes were applied by brushing (in three coats) after bisque. The tiles were fired at cone 03. This is an old classic design that I discovered when researching Damascus tile. The toughest obstacle was learning how to use Fusion 360. It turns out that cookie cutters are a starter project for many 3D software packages, there are lots of videos on making them.
Context: 3D Printing Ceramics
Wednesday 20th September 2017
Deep, deep blue without any cobalt. How?
These have to be seen to be believed, it is the deepest, richest blue we have ever produced. This is Plainsman M340 fired to cone 6. Black-firing L3954B engobe (having 10% Burnt (not raw) Umber instead of the normal 10% Zircopax) was applied inside and partway down the outsides (at the stiff leather hard stage). The incising was done after the engobe dried enough to be able to handle the piece. The glaze is Alberta Slip rutile blue. Firing schedule: Cone 6 drop-and-soak.
Context: GA6-C - Alberta Slip Rutile Blue Cone 6, Cone 6 Drop-and-Soak Firing Schedule
Wednesday 20th September 2017
Vintage boxes of Plainsman Clay found. From 1966!
M20 was for forerunner of M340. M22. We are not actually sure. Does anyone know? Would it still be good? Definitely. Just smash it up and put the dried pieces in a bucket of water to slake.
Tuesday 12th September 2017