Glaze Material Substitution

Explanation of Material Substitution

Using material substitution we can replace a material with one or more other materials that have a similar composition.

As an example, let’s look at two common glaze colorants, Cobalt Oxide and Cobalt Carbonate.

The Cobalt Oxide potters use is sold as CoO, but is actually Co3O4, while Cobalt Carbonate is CoCO3. We are interested only in the cobalt. First, let’s look up the molecular weights & mass percent of each element:
Atomic weight of “Cobalt Oxide”, Co3O4: Co = 73.423 %, O = 26.577%
Atomic weight of Cobalt Carbonate, CoCO3: Co = 49.548 %; C = 10.098 %; O = 40.354%

Handy website for looking up molecular weights.

To convert from Cobalt Oxide to Cobalt Carbonate:

  1. Calculate the ratio of the relative molecular weights of Cobalt Oxide to Cobalt Carbonate:
    73.423 / 49.548 = 1.48
  2. Multiply the amount of Cobalt Oxide in the recipe by 1.48 to get the amount of Cobalt Carbonate

To convert from Cobalt Carbonate to Cobalt Oxide:

  1. Calculate the ratio of the relative molecular weights of Cobalt Carbonate to Cobalt Oxide:
    49.548 / 73.423 = 0.675
  2. Multiply the amount of Cobalt Carbonate in the recipe by 0.675 to get the amount of Cobalt Oxide

To calculate the ratio, we can also use the percentage analysis of Cobalt Oxide and Cobalt Carbonate. Cobalt Oxide’s analysis is 93.35% CoO, while Cobalt Carbonate’s analysis is 63.00% CoO:
93.35 / 63 = 1.48
63 / 93.35 = 0.675

Example of replacing Cobalt Oxide with Cobalt Carbonate

Given the following recipe:

Leach 4321 +1% Cobalt Oxide
40  Potash Feldspar		
30  Silica		
20  Whiting		
10  Kaolin			
0.6 Cobalt Oxide	
Total:	100.6	

To convert from Cobalt Oxide:
0.6 Cobalt Oxide × 1.48 = .89 Cobalt Carbonate

New Recipe:

Leach 4321 +1% Cobalt Oxide
40  Potash Feldspar		
30  Silica		
20  Whiting		
10  Kaolin			
0.89 Cobalt Carbonate	
Total:	100.89	

Synthetic Ash

Please see Synthetic Ash

Kaolin & Calcined Kaolin

Albany Slip

For substitutions, see Albany Slip

Barnard Clay

For substitutions, see Barnard Clay

Cornwall Stone

For substitutions, see Cornwall Stone

Nepheline Syenite (Neph Sye)

For substitutions, see Nepheline Syenite

Frits

via Alisa Liskin Clausen:
JM Frit 169 gram for gram sub for both Frit 3134 and GB.

Fluxes

Magnesium

Magnesium Carbonate & Talc or Dolomite

Tom Buck via Clayart:

Original question: what will replace magnesium carbonate (MgCO3). And
David Henley asked for equalivalent values for Talc and Dolomite as substitutes.
To do the subs, one does it on a molar basis, namely,
1 mole MgCO3 sypplies 1 mole MgO in the fired glaze.
So, 1 mole of Dolomite (MgCO3.CaCO3) supplies 1 mole MgO and 1 mole CaO.
Plus a bit of “bound water”, 1.5% often.
And 1 mole Talc (MgO.SiO2) supplies 1 mole MgO and 1 mole SiO2.
Talc, however, usually has some “bound water” with the MgSiO3 (often 5.5%)
As result the weight equivalences are:
Dolomite has a mole weight 184.4, add water = 187.2
Talc has a mole weight of 100.4, add water = 102.6
MgCO3 has a mole weight of 84.3. And it usually is of high purity with no water.
So to sub for MgCO3 in a recipe: Divide the weight by 84.3 and if you use Talc multiply the answer (= to No. of moles) by 102.6. This gives the amount of Talc needed in the recipe. Then if you divide the amount of Silica (Flint) by 60 you find the No. of moles of it, and you subtract this amount by the number of moles Talc, and then using this new number of Silica/Flint moles, remulitply by 60 to find the NEW weight value for Silica/Flint.
The same applies to Dolomite only this time you adjust the amount of Whiting (or Wollastonite) in the same way.

Barium & Strontium

NOTE: May need a separate article!
There are a number of ceramicists who have experimented with replacing Barium (in the form of Barium Carbonate) with Strontium (in the form of Strontium Carbonate). However, this Material Substitution article only covers replacing materials with similar oxides, not replacing one oxide (barium) with another (strontium).

Wollastonite & Whiting

Whiting’s analysis is 56.10% CaO, while Wollastonite contains 48.28% CaO and 51.72% SiO2
For these conversions, we should also keep in mind that silica (quartz) is 100.00% SiO2.

To convert a recipe containing 10% Whiting to Wollastonite:

  1. Calculate how much Wollastonite we need to get the same amount of CaO in Whiting:
    56.10 / 48.28 = 1.16 × 10% whiting = 11.6% wollastonite
  2. Calculate how much silica is added by the Wollastonite:
    11.6% Wollastonite × .5172 (amount of silica in Wollastonite) = 6% silica added to glaze
  3. Subtract the 6% of silica added by Wollastonite from the glaze recipe. If the recipe already contains more than 6% of silica (quartz), then this will be easy. Otherwise you may need to substitute other materials that contain silica (like Talc) or just be ok with the new glaze having more silica.

To convert a recipe containing 10% Wollastonite to Whiting:

  1. Calculate how much Whiting we need to get the same amount of CaO in Wollastonite:
    48.28 / 56.10= 0.86 × 10% Wollastonite = 8.6% Whiting
  2. Calculate how much silica is lost by replacing Wollastonite:
    10% Wollastonite × .5172 (amount of silica in Wollastonite) = 5.172% silica needed
  3. Add the 5.172% of silica we lost by adding 5.172% of silica powder (quartz) to the recipe, or by including other materials that contain silica (e.g. Talc).

Čazo Čazim Mehmeti:

All we need is how much % in molar mass the observed element participates in the whole compound.
Wollastonite (CaSiO3): Si = 24.178 %; Ca 34.502 %; O: 41.320 %
Whiting (CaCO3): Ca = 40.04%; C = 12%; O = 47.96%
So:
Ca -> Whiting to Wollastonite = 40.04/34.502 = 1.16
Ca -> Wollastonite to Whiting = 34.502/40.04 = 0.86
Missing silica: (24.178 +(41.320 * 2/3) = 51.72

Soda Ash & Sodium Bicarbonate (Baking soda)

100 gr soda ash = 158.52 gr sodium bicarbonate (heat in the oven during half an hour)

Roger Graham via Clayart:

More chemistry coming up. Sodium bicarbonate is NaHCO3. It has the useful property that, when heated a bit above 100 degrees C, it decomposes and gives off steam and carbon dioxide (which of course is why they use it in cooking… the carbon dioxide given off is what makes the pastry rise). What’s left behind is just plain Na2CO3, the anhydrous kind.

Which brings us to the practical steps. If you weigh out 100 grams of baking soda into a cooking pot, and heat it on the stove or in the oven for say ten minutes, it will steam itself dry. You will end up with 63 grams of anhydrous soda ash. If you want it to remain anhydrous, better store it in an airtight jar.

Gerstley Borate

100 gr Gerstley Borate = 100 gr Crecer frit 174 , exactly the same as Ff 3134-2.
100 gr Gerstley Borate = 100 gr Colemanite

Colorants & Opacifiers

Iron

Yellow Iron Oxide and Red Iron Oxide

Yellow Iron Oxide’s analysis is 88% Fe2O3, while Red Iron Oxide’s analysis is 95% Fe2O3.

To convert from Yellow Iron Oxide to Red Iron Oxide:
88 / 95 = 0.926 x amount of Yellow Iron Oxide = amount of Red Iron Oxide
95 / 88 = 1.08 x amount of Red Iron Oxide = amount of Yellow Iron Oxide

Iron Chromate

Iron + Chrome

Cobalt

Note that suppliers may stock different grades of Cobalt Oxide and Cobalt Carbonate that may vary in composition.

Cobalt oxide’s analysis is 93.35% CoO, while Cobalt Carbonate’s analysis is 63.00% CoO.

To convert from cobalt oxide to cobalt carbonate:
93.35 / 63 = 1.48 × amount of cobalt oxide = amount of cobalt carbonate

To convert from cobalt carbonate to cobalt oxide:
63 / 93.35 = 0.675 × amount of cobalt carbonate = amount of cobalt oxide

For example, a recipe with 10 cobalt oxide would need 14.8 cobalt carbonate for the same amount of cobalt. A recipe with 10 cobalt carbonate would need 6.75 cobalt oxide.

Manganese

Manganese Carbonate’s analysis is 61.62% MnO, while Manganese Dioxides analysis is 100% MnO.

To convert from manganese oxide to manganese carbonate:
100 / 61.62 = 1.62 × amount of manganese oxide = amount of manganese carbonate

To convert from manganese carbonate to manganese oxide:
61.62 / 100 = 0.616 × amount of manganese carbonate = amount of manganese oxide

To edit?:
100 gr MnCO3 = 61.74 gr MnO
100 gr MnO2 = 89.87 MnO

Copper

Copper oxide black’s analysis is 100.00% CuO, while Copper Carbonate’s analysis is 64.40% CuO.

To convert from copper oxide black to copper carbonate:
100.00 / 64.4 = 1.55 × amount of copper oxide = amount of copper carbonate

To convert from copper carbonate to copper oxide:
64.4 / 100 = 0.644 × amount of copper carbonate = amount of copper oxide

For example, a recipe with 10 copper oxide would need 15.5 copper carbonate for the same amount of copper. A recipe with 10 copper carbonate would need 6.44 black copper oxide.

??? 100 gr copper carbonate = 64.7 red copper oxide = 72 gr black copper oxide = 113 gr copper sulphate

Čazo Čazim Mehmeti This is Copper by chemistry:

Red: Cu2O - Cu percent in oxide - 0.88819 (coeff. = 1)
Black: CuO - Cu percent in oxide - 0.79886 (coeff. = 0.8994)
Carbonate: CuCO3 - Cu percent in carb. - 0.51431 (coeff. = 0.5791)
Sulphate: CuSO4·5H2O (the pentahydrate is most common form) - Cu percent in sulp. - 0.2545 (coeff. = 0.287)

So,
100 g Red Copper Oxide =
= 0.88819 /0.79886 = 111.18 g Black
= 172.69 g Carbonate
= 348.99 g Suphate


100 g Carbonate:
= 0.51431/0.88819 = 57.91 g Red
= 64.38 g Black
= 202.08 g Sulphate

Zircopax

1g tin = 2g zircopax
(Needs to be removed, this page only concerned with replacing similar oxides, not substituting different oxides.)


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