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Tony Hansen's Thousand-Post TimeLine

I am the creator of Digitalfire Insight, the Digitalfire Reference Database and ... more


Cone 6 rutile floating blue effect lost. Then regained.

Left: What GA6-C Alberta Slip rutile blue used to look like. Middle: When it started firing wrong, the color was almost completely lost. Right: The rutile effect is back with a vengeance! What was the problem? We were adjusting firing schedules over time to find ways to reduce pinholing in other ... more

Thursday 20th October 2016

Rutile blue glaze effect completely lost! A temporary solution.

Left: 4% rutile in the Alberta Slip:frit 80:20 base. This glaze has been reliable for years. But suddenly it began firing like the center mug! Three 5 gallon buckets of glaze (of differing ages) all changed at once. We tried every combination of thickness, firing schedule, clay body, ventilation, ... more

Thursday 20th October 2016

Underglazes, engobe, a good transparent glaze and cone 03. Life is good!

The white engobe was applied by pouring at leather hard stage. The underglazes were also painted on at leather hard. The mugs were then dried, cleaned, bisque fired, dipping in clear glaze and final fired to cone 03. The clay and engobe have frit additions to make them vitrify at low temperatures.

Thursday 20th October 2016

Blistering in a cone 6 white variegated glaze. Why?

This glaze creates the opaque-with-clear effect shown (at cone 7R) because it has a highly fluid melt that thins it on contours. It is over fired. On purpose. That comes with consequences. Look at the recipe, it has no clay at all! Clay supplies Al2O3 to glaze melts, it stabilizes it against running ... more

Thursday 20th October 2016

Does it matter which transparent glaze you use over underglazes? Yes.

These porcelain mugs were decorated with the same underglazes (applied at leather hard), then bisque fired, dipped in clear glaze and fired to cone 6. While the G2926B clear glaze (left) is a durable and a great super glossy transparent for general use, its melt fluidity is not enough to clear the ... more

Thursday 20th October 2016

Laguna B-Mix on Steroids! I have wedged in 10% and 20% Plainsman P.E.S.

Both pieces have a transparent glaze, G1947U. The bar in the front is PES (Performance Enhancing Substance)! PES is made from 50:50 Plainsman A1 and St. Rose Red, it behaves like a red fireclay. BMix has some specks anyway, so why not concentrate them into some awesome aesthetics? The addition does ... more

Wednesday 19th October 2016

The silica pants of this cone 10R mug have fallen down!

This stoneware mug was glazed inside and halfway down the outside with pure silica. At some point during heatup the outside layer, not shrinking like the piece, simply fell down. And was sintered enough to hang together and remain intact through the rest of the firing (on the inside, the shrinking ... more

Wednesday 19th October 2016

Custer feldspar and nepheline syenite applied pure as a glazes. How?

The coverage is perfectly even on both. The Custer is thicker. How did I do this? Epsom salts. I slurried the two powders in water until the flow was like heavy cream. Then I added a little water to thin and started adding the epsom salts. After only a pinch or two they both gelled. Then I added ... more

Monday 17th October 2016

Pure Custer Feldspar and Nepheline Syenite on cone 10R porcelain bodies

These were applied to the bisque as a slurry (suspended by gelling with epsom salts). The nepheline is thicker. Notice the crazing. This is what feldspars do. Why? Because they are high in K2O and Na2O, these oxides have by far the highest thermal expansions. So if a glaze is high in feldspar it should be no surprise that it is going to craze also.

Monday 17th October 2016

Bamboo glaze that is actually functional

The stunning cone 10R Ravenscrag bamboo glaze (GR10-J plus 0.5% iron oxide) on a Grolleg porcelain. Up close it can feel and look like a fine wood surface (when used on a porcelain). The cone 10 recipes page at has more info.

Monday 17th October 2016

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What people have said about digitalfire

• Your glaze expertise is the piece of the clay puzzle that I need to relax and enjoy this artistic journey.

• Hi Tony, Thanks for this great project and all the info and tutorials.

• I normally do not comment on articles I find, but this is amazing. Thank you so much for providing this information! I am a ceramics student in my BFA year, and this is the most comprehensive and helpful information I have found on creating a porcelain casting slip.

• I must say I am amazed by what I saw here. I am even more surprised to see so much of cermaic material stuff here.

• Thanks for all you do for ceramics!

• The Tony of digitalfire, wow. I love the digitalfires website, but I thought it cost money to get advice from you.

• Again, thanks for building a website that has been very influential in how I look at ceramics in general, and that has been such a valuable resource to my work as a student, production potter, and chemist.

• Tony, the Boraq II substition for gerstley borate in the formula I sent you a while ago was succesful. Congratulations for figuring out boraq! I've tested Murray's, Gillespie, Laguna, IMCO, and also raw materials such as Cadycal, Ulexite, Colemanite, and the substitutes you recommended in your articles made of several components blended with Cadycal (I referred to these in my previous letter) all with varying degrees of success but only the boraq II produced results that were indistinguishable from GB. This glaze is very sensitive so I consider the test a success. It had to mess with the plasticity with additions of hectorite and ball clay.

• 'we have been using the arabia blue and white variation of the 5X20 cone 6 glaze, and have had a great response from our customers. Thanks for your efforts - you have made a believer out of me!"

• I have visited your site many times. We have the largest department in new england at the moment. I invited students to visit the school library to access your site directly for all its wisdom! You do far more good than you realize, fellow mud-diver.

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