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Absolutely jet-black cone 6 engobe on M340

Absolutely jet-black cone 6 engobe on M340

This is the L3954B engobe recipe but it has 15% Mason 6600 black body stain (instead of the normal 10% Zircopax for white). There is no cover glaze, yet it is durable and absolutely coal black (so a lesser stain % is possible). We have updated the mixing instructions at PlainsmanClays.com and Digitalfire.com pages (showing exact amounts for water, powder, Darvan) and the text on the glossary pages about thixotropy and engobes (read these again and learn to use the engobe process even better). This engobe base is designed to work on regular M340/M390 stonewares (not porcelains). This is exciting because these bodies are so much more robust in drying and much less expensive than porcelains.

Friday 13th April 2018

Close-up of Floating Blue on cone 6 dark/buff burning bodies

Close-up of Floating Blue on cone 6 dark/buff burning bodies

Originally popularized by James Chappell in the book The Potter's Complete Book of Clay and Glazes. It is loved and hated. Why? The high Gerstley Borate content makes it finicky. But the magic ingredient is not the GB, it is the rutile, Rutile makes the cobalt and iron dance. This recipe actually produces a number of different mechanisms of variegation. Color and opacity vary with thickness. Small rivulets of more fluid glass flow around more viscous phases producing micro-areas of differing colors and opacities. Titanium crystals sparkle and calcium-borate creates opalescence. Bubbles of escaping gases (from GB) have created pooling. Small black speckles from unground or agglomerated particles of iron are also present. Surprise! This is actually Ravenscrag Floating blue. All the visuals, none of the headaches.

Friday 23rd March 2018

Feldspar applied as a glaze? Yes! The way I did it will change how you glaze.

Feldspar applied as a glaze? Yes! The way I did it will change how you glaze.

Custer feldspar and Nepheline Syenite. The coverage is perfectly even on both. No drips. Yet no clay is present. The secret? Epsom salts. I slurried the two powders in water until the flow was like heavy cream. I added more water to thin and started adding the epsom salts (powdered). After only a pinch or two they both gelled. Then I added more water and more epsom salts until they thickened again and gelled even better. They both applied beautifully to these porcelains. The gelled consistency prevented them settling in seconds to a hard layer on the bucket bottom. Could you do this with pure silica? Yes! The lesson: If these will suspend by gelling with epsom salts then any glaze will. You never need to tolerate settling or uneven coverage again! Read the page "Thixotropy", it will change your life as a potter.

Friday 16th March 2018

Making ceramic tile shapes by 3D printing your own cookie cutters

Making ceramic tile shapes by 3D printing your own cookie cutters

This was done on an affordable RepRap printer. The red plastic templates 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 these cookie-cutters 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.

Saturday 24th February 2018

Matte cone 6 glazes have identical chemistry but one melts more. Why?

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.

Thursday 11th January 2018

Smash your ware to see if it is strong!

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.

Saturday 11th November 2017

Why would a low fire transparent require four frits?

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.

Thursday 9th November 2017

Match calculated COE to dilatometer-measured body COE? No!

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.

Monday 23rd October 2017

An incredible silky matte surface supports wild colors at cone 6 oxidation

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.

Thursday 19th October 2017

A black engobe transforms the floating blue glaze over it

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.

Monday 2nd October 2017

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