Fixing Cone 6 Leaches Clear - Crazing

Leach's Satin Clear Original

Total:100.00

Auto Unity Formula

Notes

This is crazing on Laguna B-mix. Neither the clay or glaze are at fault, they are simply incompatible. Still, 20% feldspar sourcing lots of KNaO plus extra KNaO coming from a frit certainly makes crazing less than a surprise for this glaze.

Concerns: It is melting enough, but has low B2O3 and it won't take much to introduce cutlery marking and leaching.

Since this is a silky matte, it will be able to accept low-expansion MgO and can afford to give up high expansion KNaO. MgO is a mechanism for matte glazes.

It might be wise to consider using the base matte at http://plainsmanclays.com/index.php?menupath=62
It can be tuned by adding glossy glaze, giving alot of control over the degree of matteness. Matteness is a fragile mechanism that needs close control and assure a compromise between functionality and appearance.

Another matte base option is G1214Z. It is a calcium matte base that is well documented on the internet (just google "G1214Z recipe".

URLs

A good adjustable base matte recipe

Pictures

Leaches clear on BMix - Crazing

Leach's Satin Clear - Craze fix

Total:100.00

Auto Unity Formula

Notes

This recipe is the product of tweaking in my Insight-live.com account. My objective was to introduce MgO (very low thermal expansion oxide) at the expense of KNaO (very high expansion).

I originally tried supplying MgO from Talc. But in this recipe I employed Ferro Frit 3249, it is a much better because it has zero-LOI, is more consistent, melts better and brings more B2O3 (that extra B2O3 is going to make the glaze melt better). Frit 3249 is a super-low expansion frit. Only small changes were needed to match up oxide levels disrupted by its introduction. The fired result looks identical on the flow tester. But if it is a little too glossy, Al2O3 levels can be raised to tune it (that would by easy in Insight-live, just lower the EPK until the calculated Al2O3 hits 0.50, then raise the SiO2 to bring it back up to 2.95).

Another helpful change that could be made is sourcing CaO using Wollastonite instead of calcium carbonate. That would really lower the LOI.

Pictures

Leach's Clear crazing adjustment

This substitutes MgO for some of the CaO and KNaO. It also adds a little more B2O3 for better melting. This melts just as good or better and appears to have about the same surface gloss. It would be a little more matte by raising the Al2O3, this would drive the expansion down even further.

Leach's clear and craze adjustment

3mm thick x 15mm square samples fired on a porcelain tile.
Left: Original
Right: Adjustment.
The surface is iddentical on this samples.

Cone 6 Magnesia Matte Base

Total:102.06

RO Unity Formula

Notes

This matte recipe was developed at Plainsman Clays. It descends from a high-dolomite recipe that was originally used to compare shipments of dolomite for consistency.

WARNING: The degree-of-matteness is very dependent on cooling rate. Fast cooling (e.g. free-fall in a lightly-loaded or smaller kiln) produces a silky matte surface. Slower cooling (e.g. a heavily loaded kiln) produces a more matte and drier surface (subject to cutlery marking). Either adapt your firing curve or adapt this recipe to your firings (e.g. if not silky enough blend in some glossy G2926B, the mixing can be done by simply pouring together, volumetrically, the two slurries).

PlainsmanClays.com documents this recipe using a variety of stains.

Comments

2017-09-06

This is a slight variation of the Master recipe wherein the Frit 3124 has been increased, and the Flint Silica quantity is slightly higher.

G2934W has 4% tin oxide.

This is based on the 3728, a recipe that we use to compare new shipments of dolomite. However this raises the Al2O3 and SiO2 to the same levels as G2928C Ravenscrag matte.

URLs

Prepared public do..om Plainsman Clays

Pictures

G2934 with Hemlock Green, Pansy Purle Stains

10 gram balls have been melt down onto a tile at cone 6.
Top: G2934 with normal flow
Left: 8% 6213 Hemlock Green. Needs significant flux.
Right: 8% 6305 Violet stain. Flowing a little less, needs a little flux.

True mattes should still be matte if overfired

The G2934 is a high-MgO matte, it melts well and does not cutlery mark or stain easily. As evidence that it is a true matte, notice that it is still matte when fired to cone 7 or 8. VC71, while having a similar pleasant silky matte surface at cone 6, converts to a glossy if fired higher (suggesting that its cone 6 matteness is due to incomplete melting). For the same reason the VC71, it is whiter in color (but as soon as it begins to melt and have depth the color darkens).

G2934 + 5% Titanium thinner/thicker on M390

Cone 6 Calcium Matte Base

Total:101.00

Auto Unity Formula

Notes

This is the same as G1214Z but splits the kaolin to a mix of calcined and raw (to cut drying shrinkage).

I made 3000 grams and used 2600 water to get 1.45 specific gravity and good flow properties (no epsom salts needed).

Pictures

Alternate Code Number:GS6-B

XML (to paste into Insight)

<?xml version="1.0"?> <recipes version="1.0" encoding="UTF-8"> <recipe name="Cone 6 Calcium Matte Base" id="156545" key="B4SqyLpu" date="2019-05-31" codenum="G1214Z1" picturebasename=""> <recipelines> <recipeline material="Wollastonite" amount="27.000"/> <recipeline material="Ferro Frit 3124" amount="36.000"/> <recipeline material="EPK" amount="20.000"/> <recipeline material="Silica" amount="5.000"/> <recipeline material="Calcined Kaolin" amount="13.000"/> </recipelines> </recipe> </recipes>

Born: 1998-04-21, Modified: 2019-05-31 12:17:54