Comment

Comment by Norm Stuart on November 3, 2015 at 2:00pm

Magruder Red has a lot of incarnations, with our slow-cooling schedule (50F per hour between 1800 F and 1500 F)  and various additions.

As does Marsala (not shown) with the same changes and additions)

Bright red with synthetic iron oxide

.

A more translucent red when replacing the Bone Ash and some of the Red Iron Oxide with Iron Phosphate

.

Ugly brown with impure red iron oxide

.

An interesting blend of tan and brown with 10% Ferro Frit 3134

.

And a sparkling brown with 10% Ferro Frit 5301

Comment by Norm Stuart on November 3, 2015 at 1:49pm

Brenda - The Stephen Hill cooling schedule is slightly different to ours. I believe Hill cools between 1,700 F and 1,500 F at 40 F per hour for 5 hours.

Our cooling schedule is a little faster over a slightly bigger range - between 1,800 F and 1,500 F at 50 F for 6 hours.

We use G200 Feldpsar (Potash Feldspar) for the Clear Blue, now that our bag of Kona is gone. With the G200 the Clear Blue is always shows the white areas creating a light blue - often on porcelain almost the entire glaze field has become predominantly white crystals becoming the "light blue".

Water Color Blue and Water Color Green are some of the few glazes which become quite unattractive with our cooling schedule.

The Water Color Green becomes matte and the Water Color Blue becomes a crystallized brownish-black.

Another is "Clear Base Blue" which varies greatly both by it's cooled and how much iron is contained in the clay it's applied to. As with other slow-cooling duds, adding 10% Ferro Frit (3269, or 3134, or 5301) can suddenly make it interesting again.

Comment by Brenda B Hardt on November 3, 2015 at 12:55pm

Not having Kona Feldspar, I made a test batch using Minspar in same percentage.  I also tested the Warm Jade. I fired to Stephen Hil's slow cool schedule programming my kiln to a max temp of 2160F which under-fired so that cone only bends over to 2 o'clock. This is enough for the WaterColor Green with SCM warm base to form some mini crystals but I will increase to 2175 and try again..

I did not get the depth, it is a rather smooth clear blue and did not run so I like it.  The Warm Jade looks lovely though not with interesting spots. Hoping to add this picture: the first time I have posted a test! (Note, the S&C note on the test tile means I put 2 black lines of Stroke and Coat there to test the transparency factor.)  I can't wait to try them layered on each other and over a warm base.

Comment by Joseph Fireborn on November 3, 2015 at 11:44am

Very nice. Super glossy and has nice detail under it.

Comment by Randy McCall on November 3, 2015 at 8:59am

Got to try the clear Blue.  Also the combo of Warm Jade Green with it.  My kind of glazes.  Clear Blue appears to be a good layering glaze and that's what I am after.

Comment by Norm Stuart on October 27, 2015 at 10:38am

Randy - I suspect Clear Blue is simply that, a translucent blue without a slow-cool.  I would guess that the white flecks in this glaze are crystallization forming during the slow-cool.

I have no way of knowing myself because everyone at our studio now expects the results of our 50 F per hour slow-cool between 1,800 and 1,500. So that's how our kiln is fired now.

Initially during the first two years we would fire a Cone 6 without a slow-cool once there was enough for a kiln load, but it's now year five and everyone has lost interest in fast cool.  Often when someone wanted to create the look of a fast-cool glaze, they had also used another glaze on their piece on which they wanted the slow-cool look - which of course is not possible.

I've had adjust some glazes. As an example the Zinc Semimatte in "Mastering Cone 6 Glaze" crawls badly when cooled at 50 F per hour rather than the 185 F per hour the book recommends.  This requires extra flux to thin the glaze, like adding 10% to 20% Ferro 3134 frit which is extra glass and flux.

Adding 10% to 20% Ferro 3269 with Fluorine and Zinc, or 5301 with a lot of Fluorine, usually creates an entirely new glaze, often with sparkling crystals. It's now always a winner, but it's always worth the trial.

Many glazes when fired to Cone 6 with a fast cool, come close to the look of a slow-cooled Cone 6 firing when subsequently refired in a Cone 04 bisque firing (1,888 F), which essentially gives the glaze additional crystallization time in the 1,800 F to 1,500 F range.

Some fast cooled glazes, like Amaco Seaweed a clear with green strands running through it, become opaque when slow-cooled so I need a completely different recipe to create that effect.

The tile with Clear Blue over your Warm Jade would likely look the same fast-cooled, and it simply looks like the result of thermal and density mixing. I've found adding a layer of clear over the top of one glaze layer over another often helps create this marbleized look.

One of the most overlooked factors in how a glaze looks is the layer of interaction between the glaze and the bisqued clay. We typically have 8 different types of clay available so unless I do a test tile I can end up surprised.

Comment by Randy McCall on October 27, 2015 at 5:07am

Norm what happens when you don't slow cool this glaze?

Comment by Norm Stuart on October 26, 2015 at 7:06pm

Brenda -

G200 Feldspar has been replaced by G200-HP which has a higher potassium content. For years Imerys North America which mined and sold G200 was mixing their G200-HP with a local soda feldspar until they depleted the soda feldspar mine, and now they only sell G200-HP.

Laguna Clay and many suppliers still offer G200-Old Blend by mixing 70% G200-HP (predominantly potassium feldspar) with 30% Minspar (predominantly soda feldspar), just as Imerys did with their own soda feldspar previously.

Other suppliers are selling a G200 feldspar substitute from Spain.

Custer Feldspar is also not that different from old G200 chemistry.

http://digitalfire.com/4sight/material/g-200_feldspar_800.html

http://digitalfire.com/4sight/material/g200_hp_feldspar_3054.html

http://digitalfire.com/4sight/material/g200_old_blend_feldspar_3186...

http://digitalfire.com/4sight/material/custer_feldspar_253.html

We had very old bags of material from an earlier incarnation of our studio, so we were actually using Kona Feldspar for this tile, but we're now using the Laguna G200-Old Blend and I don't see a difference.

Comment by Brenda B Hardt on October 26, 2015 at 6:33pm

So guessing G200 is mined out too?  I was given a recipe for Bird Matt that calls for G200.

Would I use same amount of Minspar in the CLEAR BLUE recipe as Kona or use the Insight software to calculate a different amount ?

Comment by Norm Stuart on October 26, 2015 at 5:40pm

Clear Blue with Minspar layered over Randy McCall's Warm Jade

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