Sandstone – wikipedia

And sandstone enamel is a high temperature ceramic enamel. The enamels composed in the ceramist’s workshop have a huge palette of glazes, textures and colors. In addition, the diversity of possible overlays enrich the results in the buzz.

However, the chemical compounds that constitute them are reduced to a few raw materials: it is by playing on their proportions that the craftsman creates different enamels.

Daniel de Montmollin’s work ^{[ first ]} oriented the investigations of many artists. He determined the possible chemical combinations and those to be excluded (bad fusion, unsightly appearance, unequal matter etc.). In his reference article “Practice of enamels 1 300 °C “, His experiments are schematized by a hundred diagrams.

Daniel de Montmollin works according to chemical formulas: his enamels are identified in additions of molecules. One of her disciples, Lisa Brizzolara, has transcribed her experiences into recipes for marketed products from which she concretely established the molars. His formula/recipe conversion spreadsheets greatly facilitate the decryption of the experiences of Taizé’s brother. ^{[Ref. necessary]}

The object being the sandstone, the cooking means “high temperature”, on average 1 280 °C . Many paths are possible to reach this point: temperature rise duration, number of levels, cooling time, oven atmosphere (reducing or oxidizing) etc. The way of conducting cooking is decisive for the final appearance of the glaze.

The formula of an enamel can be analyzed in three elements:

The molecules of the basic ingredients are chemically composed of one or more metallic elements and an oxygen atom (simple metal oxide), and therefore written in the “RO” form. They act as fondants.

ex. : ZNO, MNO, KNAO (present in feldspath), CAO (present in lime), MGO etc.

Amphotères have both basic characters and acidic characters. These are trioxides, chemically made up of two metal atoms and three oxygen atoms, in the form “r” ₂ O ₃ ».

ex. : B ₂ O ₃ , Al ₂ O ₃ etc.

Acid ingredients are metallic dioxides and are therefore written “Ro ₂ ».

ex. : It’s not ₂

From the chemical formula to the supplier’s catalog [ modifier | Modifier and code ]

In marketed products, these chemical elements are in a mixture.

ex. : In the feldspath, we find in particular Sio ₂ , Al ₂ O ₃ , Na ₂ O and k ₂ O (Recombinés in Knao).

Zno, Mno, Knao, MGO are mixed in silica

On the other hand, Cao is alone in lime.

Wollastonite is made up of CAD and SIO ₂ .

To correct a recipe formula, it is necessary to consider that the total of the basic ingredients equal 1 (a mole). An enamel never has less than 1.5 mole of silica for a basic mole.

The following example is only a hypothesis which makes it possible to understand how we compose an enamel and the necessary weight of each of the products, according to the chemical elements which constitute them:

Formula	Base	Apopheros	Acid
The Wollastonite Aporte high et si0 2 in almost equal parts ⇒	0.4 high		0,48 is not 2
Zinc oxide	0,2 ZnO
The potassium feldspath provides 1 knao + 1.05 al 2 O 3 + 6,35 is not 2 ⇒	0,4 cum	1,05 Al 2 O 3	6,35 is not 2
Base = 1 mole	first
We add 3 parts of silica To obtain a total report of 1 alumina / 10 silica			3 is not 2
The kaolin brings 1 share of al 2 O 3 and 2 parts of SIO 2		0,2 Al 2 O 3	0,4 is not 2
	Total =	1,25 Al 2 O 3	10,23 is not 2

Recipe	Quantity (in moles)	Multiplied by molecular weight (in grams per mole)		Result (in grams)
Wollastonite	0.4	100	→	40
Feldspar	0.4	577	→	230
Zinc oxide	0.2	81	→	16
Silica	3	sixty one	→	183

It is this formula conversion work/recipe that Lisa Brizzolara has done for a wide range of classified enamels among tenmoku, iron red, oil drops, celadon, white magnesian, rutile and titanium enamels.

The following table identifies the amplitude of the combinations of possible products, the total of each recipe to total 100, with the exception of the rutile and the titanium which are in addition.

Type	Feldspar	Lime	Talc	Kaolin	Silica	Bone ash	Iron oxide	Comments
Tenmoku	0 to 93	0 to 31	0	0 to 31	0 to 31	0	7	Light brown to almost black. Result more nuanced in reducing cooking and on a textured shard. Excellent under layer.
Magnesian white	11 to 24	8 to 16	11 to 24	10 to 43	26 to 27	0	0	Opaque, covering, animated. Yellow reflections thanks to magnesia.
Red -red	47 to 53	3	6 to 7	4 to 8	14 to 24	6 to 7	10 to 11	Copper reflections at the vermilion, nuanced brown.
Oil drops	57 to 68	2 to 5	4 to 8	1 to 8	0	2 to 22	6 to 9	Exclusively oxidizing cooking. Black to purple stain on a red to brown background.
Celadon	0 to 97	0 to 33	0	0 to 33	0 to 31	0	3	Exclusively reductive cooking.
From white to yellow	18 to 47	11 to 26	3 to 16	6 to 18	24 to 34	0	0	+ 8 to 20% titanium
From white to pink	18 to 47	11 to 26	3 to 16	6 to 18	24 to 34	0	0	+ 8 to 20% rutile

The game of combinations widens the range of the few enamels seen previously. The following photos illustrate the possible overlapping of glazes.

However, it should be kept in mind that when it applies three layers of enamels, the ceramist must have the gesture sufficiently prete to not exceed 1.5 mm thick – check with a handle needle.
The thicker the enamel, the more slow the temperature rise and/or include levels.

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  White Magnesian on Tenmoku

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  Magnesian white / titanium / oil drops

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  White Magnesian on iron

Iron oxide enamels are an excellent underlay. The iron dates back to the surface during the merger by forming spots, rings, reflections. In the third passage, the White Magnesian reveals new shades. He gains to be applied to certain areas and not to the entire room.

Notes and references [ modifier | Modifier and code ]

Bibliography [ modifier | Modifier and code ]

• Elisabeth Lambercy, Ceramic raw materials and their fire transformation , Banon, clay, coll.  « Granit », 1993 , 510 p. (ISBN  2-909758-08-7 ) .

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