Researching the Iron Oxide/Tricalcium Phosphate Dynamic in a Cone 10R Matte

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

Research we did to study varying percentages of these on the fired color and surface character


Project Name

Red Mustard Glaze Development

Project Codenumber

UnAssigned

Notes

Yellow and Red Mustard glazes were used in the Plainsman Clays studio for many years but we stopped because they were crazing (because of the high feldspar content) and the surface did not seem functional (it was easily cutlery marked). However we often get recipe requests for this type of glaze. On revisiting these two I noticed that they have the same recipe (except for the percentage of tricalcium phosphate and iron oxide). The red has more of both. But is it because of higher iron or higher trical?

Some people might call this red glaze an "iron red", but I have not used that term as I do not believe it applies. At cone 10R, 10-12% iron oxide in a transparent will saturate in the melt and precipitate during cooling to produce vivid maroon to red colored crystals. That is not what this glaze is.

To investigate my plan is to test if this mechanism will also work in our G2571A base matte recipe. G2571A does not craze and has a very functional surface. Its Si:Al ratio is higher and proportions of fluxes are quite different (much more MgO, less CaO and KNaO). And it has a little boron.

If G2571A does not work I will adjust its chemistry to be more like the original 77E14A and try again.

RED MUSTARD 10R

Code #

77E14A

Materials Amt
Potash Feldspar 46.300
Talc 3.800
EPK 21.700
Tricalcium Phosphate 3.800
Calcium Carbonate 18.800
Additions Amt
Red Iron Oxide 5.700

Total:100.10

Auto Unity Formula

CaO 0.66
MgO 0.09
K2O 0.25
(KNaO) 0.25
P2O5 0.04
Al2O3 0.48
SiO2 2.07
Fe2O3 0.10

Ratios

Si:Al: 4.3:1
R2O:RO: 0.2:0.8

Expansion

8.8 (Molar:8.1)

LOI

12.6

Cost

0.45 per kg

Notes

*This was the recipe we used many years ago. People like the red-breaking-to-yellow and yellow flecks (likely larger iron silicate crystals) on a red background.

This calculates to a very high thermal expansion so crazing is very likely on most clay bodies.

The red color appears to be a product of the iron and 4% tricalcium phosphate. Only a small amount of the yellow remains on the edges of contours where it thins.

Pictures

Red Mustard cone 10R bowl

Typecodes

RCP-Undefined

Alternate Code Number:GS10-L

XML (to paste into Insight)

<?xml version="1.0"?> <recipes version="1.0" encoding="UTF-8"> <recipe name="RED MUSTARD 10R" id="63510" key="yXQ359X5" date="2021-11-16" typecodes="RCP" codenum="77E14A" picturebasename=""> <recipelines> <recipeline material="Potash Feldspar" amount="46.300" tolerance=""/> <recipeline material="Talc" amount="3.800" tolerance=""/> <recipeline material="EPK" amount="21.700" tolerance=""/> <recipeline material="Tricalcium Phosphate" amount="3.800" tolerance=""/> <recipeline material="Calcium Carbonate" amount="18.800" tolerance=""/> <recipeline material="Red Iron Oxide" amount="5.700" added="true"/> </recipelines> </recipe> </recipes>

Born: 1990-02-13, Modified: 2021-11-16 21:39:55

YELLOW MUSTARD 10R

Code #

77315A

Materials Amt
Potash Feldspar 52.000 50.00%
Talc 4.000 3.85%
EPK 25.000 24.04%
Tricalcium Phosphate 2.000 1.92%
Calcium Carbonate 21.000 20.19%
Additions Amt
Red Iron Oxide 4.000 3.85%

Total:108.00

Auto Unity Formula

CaO 0.64
MgO 0.09
K2O 0.26
(KNaO) 0.26
P2O5 0.02
Al2O3 0.52
SiO2 2.22
Fe2O3 0.07

Ratios

Si:Al: 4.3:1
R2O:RO: 0.3:0.7

Expansion

8.7 (Molar:8.0)

LOI

12.8

Cost

0.38 per kg

Notes

*This was a stock glaze used many years ago. It fired to a similar surface to the red mustard, but was yellow. There are some red patches (or flecks). The red likely means that the iron is beginning to approach the zone where it can crystallize red (the tricalcium phosphate could be the catalyst for that).

This has the same base recipe as the red mustard. The Si:Al ratio is very low.


Also code 84-G-2-G

Pictures

Typecodes

RCP-Undefined

Alternate Code Number:GS10-K

XML (to paste into Insight)

<?xml version="1.0"?> <recipes version="1.0" encoding="UTF-8"> <recipe name="YELLOW MUSTARD 10R" id="63511" key="bXFRCAyf" date="2021-11-16" typecodes="RCP" codenum="77315A" picturebasename=""> <recipelines> <recipeline material="Potash Feldspar" amount="52.000" tolerance=""/> <recipeline material="Talc" amount="4.000" tolerance=""/> <recipeline material="EPK" amount="25.000" tolerance=""/> <recipeline material="Tricalcium Phosphate" amount="2.000" tolerance=""/> <recipeline material="Calcium Carbonate" amount="21.000" tolerance=""/> <recipeline material="Red Iron Oxide" amount="4.000" added="true"/> </recipelines> </recipe> </recipes>

Born: 1990-02-13, Modified: 2021-11-16 18:23:47

Red Mustard in G2571A Base #1

Code #

G3918

P Materials Amt
Wollastonite 5.500
Custer Feldspar 28.500
EPK 28.000
Silica 15.000
Dolomite 19.000
Gerstley Borate 4.000
P Additions Amt
* Red Iron Oxide 6.000
TriCalcium Phosphate 4.000

Total:110.00

Auto Unity Formula

CaO 0.57
MgO 0.30
K2O 0.09
Na2O 0.05
(KNaO) 0.13
P2O5 0.04
B2O3 0.04
Al2O3 0.42
SiO2 2.34

Ratios

Si:Al: 5.6:1
SiB:Al: 5.7:1
R2O:RO: 0.1:0.9

Expansion

6.7 (Molar:6.5)

LOI

14.5

Cost

0.27 per kg

Notes

*Will this better base host the visual effects as well as the original high-feldspar one?

This has higher Si:Al, and alot more MgO. Hopefully neither of these are hostile to the color development.

If this does not work it would be worth studying why. It could be because of inadequate Al2O3, that will be easy to adjust. It might be inadequate KNaO (unlikely since this one has good melt fluidity). It might be that MgO is hostile to the mechanism, again I think that is unlikely.

Pictures

Typecodes

RCP-Undefined

Alternate Code Number:GS10-L

XML (to paste into Insight)

<?xml version="1.0"?> <recipes version="1.0" encoding="UTF-8"> <recipe name="Red Mustard in G2571A Base #1" id="188780" key="pZQbAYZs" date="2021-11-16" typecodes="RCP" codenum="G3918" picturebasename=""> <recipelines> <recipeline material="Wollastonite" amount="5.500" tolerance=""/> <recipeline material="Custer Feldspar" amount="28.500" tolerance=""/> <recipeline material="EPK" amount="28.000" tolerance=""/> <recipeline material="Silica" amount="15.000" tolerance=""/> <recipeline material="Dolomite" amount="19.000" tolerance=""/> <recipeline material="Gerstley Borate" amount="4.000" tolerance=""/> <recipeline material="Red Iron Oxide" amount="6.000" added="true"/> <recipeline material="TriCalcium Phosphate" amount="4.000" added="true"/> </recipelines> </recipe> </recipes>

Born: 1990-02-13, Modified: 2021-11-16 21:43:28