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 mechanism
s 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
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. Craze
d 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
, 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
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
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
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
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