Better to mix your own cover glazes for production?
Yes. In this case the entire outside and inside of the mug need an evenly applied coat of glaze. In production, it would not make sense to attempt this by painting. For these reasons: Cost, quality, convenience. The right pail has 2 gallons of G2934 base with 10% Cerdec yellow stain: $135. Cost of jars with the same amount: Almost $300! And you have to paint them on in three coats with drying in between. The one in the pail is a true dipping glaze (unlike dipping glazes sold by glaze manufacturers that dry slowly and drip-drip-drip just like brushing ones). This one dries immediately after dipping in a perfectly even layer (if mixed according to our instructions). And a bonus: This pail can be converted to a brushing version using CMC gum.
Context: G2934Y - Cone 6 Magnesia Matte Low LOI Version, G2934 - Matte Glaze Base for Cone 6, Where Do I Start?, Brushing Glazes
Tuesday 17th April 2018
Twenty six bodies. Porcelains and native. Which do I like best?
I am testing runs of clays we (Plainsman Clays) make for potters. We are doing too many small-run products, bodies that we want to discontinue because others we are really good at making are much better. I am using native bodies and porcelains but the native ones will turn out best. I got lots of s-cracks on the porcelains, the low humidity at this time of the year caught me by surprise. But I got zero cracks on native bodies. And I am using engobes on the natives, these can turn even a dark colored stoneware surface pure white (I am also using a black engobe here). I'll use a mix of base and cover glazes that I make myself (using recipes we publish) for food surfaces and decorate some using bottled commercial glazes.
Monday 16th April 2018
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.
Context: L3954B - White Cone 6 Engobe for Plainsman M390, M340, L3954B engobe page at PlainsmanClays.com, Engobe, Thixotropy
Friday 13th April 2018
Roasting Alberta Slip at 1000F
Roasted Alberta Slip (right) and raw powder (left). These are thin=walled 5 inch cast bowls, fired to 1000F and held it for 30 minutes. Why calcine? Why 1000F? Because Alberta Slip is a clay, it shrinks on drying. Roasting eliminates that, a 50:50 raw:roast mix works well for most recipes having high percentages. And 1000F? Calcining to 1900F sinters particles together (creating a gritty material) while 1000F just does not. But note the difference: The raw powder has an LOI of 9% (looses 9% weight on firing). 1900F-calcine has zero%. 1000F-roast has only 3%. So we need 6% less (9%-3%) of it than of the raw to supply the same chemistry. For example, if a recipe calls for 1000 grams of Alberta Slip: Use 500g raw and 456g 1000F roast (500*.94).
Context: Alberta Slip 1900F Calcined, Alberta Slip 1000F Roasted, GA10x-A - Alberta Slip Base for cone 10 oxidation, GA6-A - Alberta Slip Cone 6 Amber Base Glaze, GA6-C - Alberta Slip Rutile Blue Cone 6, GA10-B - Alberta Slip Tenmoku Cone 10R, GA10-D - Alberta Slip Black Cone 10R, GR10-E - Alberta Slip:Ravenscrag Cone 10R Celadon, GA6-D - Alberta Slip Glossy Brown Cone 6, L3341B - Alberta Slip Iron Crystal Cone 10R, GA6-G - Alberta Slip Lithium Brown Cone 6, GA10-A - Alberta Slip Base Cone 10R, GA6-G1 - Alberta Slip Lithium Brown Cone 6 Low Expansion, GA6-A - Alberta Slip Cone 5 Reduction Base Glaze, GA6-F - Alberta Slip Cone 6 Oatmeal, GA6-H - Alberta Slip Cone 6 Black, Calcine, Calcination
Thursday 29th March 2018
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.
Context: Gerstley Borate, Rutile, GA6-C - Alberta Slip Rutile Blue Cone 6, GR6-M - Ravenscrag Cone 6 Floating Blue, G2587 - Floating Blue Cone 5-6 Original Glaze Recipe
Friday 23rd March 2018
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.
Context: Epsom Salts, Suspending pure feldspar and applying it as a glaze, Pure Custer Feldspar and Nepheline Syenite on cone 10R porcelain bodies, Thixotropy, Powdering, Cracking and Settling Glazes
Friday 16th March 2018
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.
Context: 3D Printing Ceramics
Saturday 24th February 2018
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