G2934 Cone 6 Matte Base Glaze and Variants

Share from Insight-live.com (Lab Documentation and Calculation System) by Digitalfire

Left column is the original, and widely used recipe (with dolomite). Center is the newer version that sources the MgO from talc and a frit instead (with a number of advantages). The right version has a higher thermal expansion and smoother surface.

Cone 6 Magnesia Matte Base

Code #


Materials Amt
Ferro Frit 3124 19.400 19.01%
EPK 18.300 17.93%
Dolomite 23.500 23.03%
Silica 26.960 26.42%
Calcined Kaolin 13.900 13.62%


RO Unity Formula

CaO 0.54
MgO 0.39
Na2O 0.06
(KNaO) 0.06
B2O3 0.12
Al2O3 0.45
SiO2 2.71


Si:Al: 6.0:1
SiB:Al: 6.2:1
R2O:RO: 0.1:0.9






66.21 per kg


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.



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.


Prepared public do..om Plainsman Clays


G2934 Matte vs. LA Matte

LA Matte has been popular for many years. However as seen here, it is not stable in the kiln because it is a zinc matte that depends on crystallization during cooling to create the surface. 2934 is an MgO matte, it is much more stable and has a better surface that does not cutlery mark nearly as bad.

G2934 Matte vs. 2928C Ravenmatte

These two have very similar chemistries. The 2928C uses as much Ravenscrag slip as possible yet still have the same chemistry as the well known Moore's matte recipe. While it appears whiter here, this is because it contains 10% zircon, normally it would be darker because of the iron in Ravenscrag Slip.

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).


C6-Cone 6 Glaze

XML (to paste into Insight)

<?xml version="1.0"?> <recipes version="1.0" encoding="UTF-8"> <recipe name="Cone 6 Magnesia Matte Base" id="56852" key="R97ta212" date="2019-03-20" typecodes="C6" codenum="G2934" picturebasename=""> <recipelines> <recipeline material="Ferro Frit 3124" amount="19.400"/> <recipeline material="EPK" amount="18.300"/> <recipeline material="Dolomite" amount="23.500"/> <recipeline material="Silica" amount="26.960"/> <recipeline material="Calcined Kaolin" amount="13.900"/> </recipelines> </recipe> </recipes>

Born: 2014-03-21, Modified: 2019-03-20 21:51:20

G2934 Low-LOI Variant

Code #


Materials Amt
Ferro Frit 3249 10.000
Nepheline Syenite 10.500
Wollastonite 21.500
Talc 14.000
EPK 20.500
Silica 13.000
Calcined Kaolin 10.500


Auto Unity Formula

CaO 0.54
MgO 0.40
K2O 0.02
Na2O 0.05
(KNaO) 0.06
B2O3 0.12
Al2O3 0.45
SiO2 2.73


Si:Al: 6.1:1
SiB:Al: 6.4:1
R2O:RO: 0.1:0.9






32.70 per kg


This is an "MgO matte". High MgO content is a common matting mechanism at cone 10 but also works at cone 6. This recipe has the same chemistry as G2934, however it sources the MgO from a frit and talc rather than from dolomite. The frit has a predictable chemistry, produces a much lower LOI (3.8 vs. 13.6), a smoother fired surface and better melt fluidity to host stains (stains look fantastic in this base).

WARNING: Like the original, 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 matter and drier surface (subject to cutlery marking). Test in your circumstances to decide whether to adjust your firing to accommodate this or blend in some glossy G2926B produce the silky surface.

Fusion Frit F-69 can be used instead of Ferro Frit 3249 (actually, it is better). This recipe employs a mix of calcined and raw kaolin to keep the drying shrinkage down (to avoid cracking on drying). If you use pure kaolin it will likely crack during drying. If you do not have calcined kaolin just make your own (bisque fire a container of powder).

This glaze has a very low thermal expansion and will not craze an any common clay body. It accepts stains exceptionally well.

We recommend doing cutlery marking tests on your ware. If they mark, blend in a little transparent glossy glaze (like G2926B). This will compromise the matteness a little but will reduce the marking.

Again, although matte in appearance, this glaze has a high melt fluidity. That means that brush-on colors could bleed.

1100 water, 1000 powder to get creamy mix.
Regular 2934 (with dolomite) took more water, about 1300. Nicer surface than G2934, same matteness, better fluidity.

Joe: April 29/19 Mixed up a batch of this glaze and added 10% Mason #6021 Red stain. Final totals were:
G2934Y + 10% stain weighed 5045 grams.
Water weighed 5450 grams.
Let glaze sit for 3 days to saturate before adding final water to bring to a S.G. of 1.43 and viscosity was approx. 12 seconds with ford cup.
At these quantities, the final ratios would be:
Glaze powder (including stain) 48%
Water 52%
This mixture yielded about 7.3 litres of mixed glaze. This glaze was screened 80 mesh and has no Epsom salts added.


G2934Y plus 8% Cerdec orange stain on Polar Ice, P300

The stain is #239616 encapsulated. The silky surface is stunning. The color is brighter on whiter porcelains.

G2934Y vs. G2934 melt flow balls

10 gram balls were melted down onto these tiles at cone 5.5.
On darker clay bodies the glaze is translucent. For white on this type of clay body a zircopax addition would be needed.

G2934Y vs G2934 melt flow test

The difference is quite amazing. The chemistry is the same. But the MgO is much more readily released from its source materials in the Y version. Also, even thought the melt is more fluid, it is still just as matte. Part of the reason for the extra fluidity could be the much lower entrained micro-bubble population in the Y (these possibly impeding the flow of the dolomite version on the left).

G2934Y matte with Cerdec red, orange stains

8% stain in each. Cone 6. Drop and hold firing. The surface quality is truly stunning!

G2934Y matte on M370 - cup

Surface very pleasant and finer than the standard G2934.

G2934 (left) vs G2934Y (right) at cone 6

G2934Y with brushwork decoration - By Ingeborg Koot

It is not bleeding significantly because the glaze has not been applied too thick.


C6-Cone 6 Glaze


16 - Yellow

1680 dry and 1400 water produced SG of 1.44. Pretty thick, added a little darvan.

239616 - Orange

Cerdec stain. Required no Epsom salts at 1.43 SG. Joe: Aug.2/18 Made a batch of this glaze: Total Powder 3400 grams Total Water 4000 grams S.G via Viscometer 1.417 Viscosity via Ford Cup 12

4 - Overglaze Blue

Test this as a brush-on color for using over G2934Y. We should demonstrate to customers how to fine tune the melt fluidity of an overglaze color and how to mix it with gum to make it paintable.

6000 - Shell Pink

Joe: Aug.8/18 made a batch using same percentages as when I made a batch of the Orange version on Aug.2/18. Total Powder: 2500 grams Water: 2946 grams. S.G. vis Viscometer was 1.401 Viscosity Ford

6213 - Hemlock Green

A little dark. Very intense. Mixed 110 water to 100 dry (3575/3250) to get 1.43 SG.

6304 - Purple

6364 - Baby Blue

3380 powder, 2800 water. 1.43 SG. Worked perfectly.

6700 - White

Pink - Mason 6020

XML (to paste into Insight)

<?xml version="1.0"?> <recipes version="1.0" encoding="UTF-8"> <recipe name="G2934 Low-LOI Variant" id="113976" key="97PD6oe3" date="2019-04-29" typecodes="C6" codenum="G2934Y" picturebasename=""> <recipelines> <recipeline material="Ferro Frit 3249" amount="10.000"/> <recipeline material="Nepheline Syenite" amount="10.500"/> <recipeline material="Wollastonite" amount="21.500"/> <recipeline material="Talc" amount="14.000"/> <recipeline material="EPK" amount="20.500"/> <recipeline material="Silica" amount="13.000"/> <recipeline material="Calcined Kaolin" amount="10.500"/> </recipelines> </recipe> </recipes>

Born: 2014-03-21, Modified: 2019-04-29 13:05:01

G2934 Higher Expansion Variant

Code #


Materials Amt
Fusion Frit F-69 7.500
Ferro Frit 3110 21.000
Wollastonite 15.000
Talc 14.500
EPK 20.000
Silica 7.000
Calcined Kaolin 15.000


Auto Unity Formula

CaO 0.44
MgO 0.40
K2O 0.02
Na2O 0.15
(KNaO) 0.17
B2O3 0.12
Al2O3 0.45
SiO2 2.81


Si:Al: 6.3:1
SiB:Al: 6.5:1
R2O:RO: 0.2:0.8






17.69 per kg


The G2934 and G2934Y have very low thermal expansions. That is good to prevent crazing but it can cause shivering. This version of the glaze increases KNaO (sourcing it from Ferro Frit 3110) at the expense of CaO.

This change has the additional effect of making the matte surface physically smoother and more bone-like. It does cutlery mark somewhat, but is quite striking.

The Fusion Frit F-69 is the same chemistry as Ferro Frit 3249.


Very smooth yet stony matte G2934Y2 Cone 6

Cutlery marks but almost cleanable. On M370.
Surface porcelain like, almost invisible on ware are first glance.

G2934Y2 matte on outside of polar ice piece


C6-Cone 6 Glaze

XML (to paste into Insight)

<?xml version="1.0"?> <recipes version="1.0" encoding="UTF-8"> <recipe name="G2934 Higher Expansion Variant" id="143110" key="SBZakDMx" date="2018-12-11" typecodes="C6" codenum="G2934Y2" picturebasename=""> <recipelines> <recipeline material="Fusion Frit F-69" amount="7.500"/> <recipeline material="Ferro Frit 3110" amount="21.000"/> <recipeline material="Wollastonite" amount="15.000"/> <recipeline material="Talc" amount="14.500"/> <recipeline material="EPK" amount="20.000"/> <recipeline material="Silica" amount="7.000"/> <recipeline material="Calcined Kaolin" amount="15.000"/> </recipelines> </recipe> </recipes>

Born: 2014-03-21, Modified: 2018-12-11 16:11:59