Bone Ash

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Bone ash is made from selected chosen bones properly leached, ground, chemically treated, calcined by a special procedure and milled to a fine particle size. Use in grounds and for adding texture and body to oil paints.

Bone ash is made from selected bones properly leached, ground, chemically treated, calcined by a special procedure and milled to a small particle size. Our bone ash is obtained by roasting degelatinized bone up to a temperature of approximately 1100° C. Afterwards, the bone ash is cooled and ground to a fine particle size so that a minimum of 95% will pass through a 325-mesh (U.S. Standard) sieve or through a 20-mesh sieve for 20 mesh bone ash. The excellent properties of bone ash is attributed to the internal structure of the small, individual particles. The original cellular structure of the bone is preserved, thus giving the material a high resistance to heat transfer (natural thermal insulator). Bone ash is primarily tri-calcium phosphate or a form of calcium hydroxyapatite.

Bone ash has the following intrinsic properties:

• Has excellent non-wetting properties
• Is chemically inert and free of organic matter
• Has high resistance to heat transfer (natural thermal insulator)

In painting grounds, it makes a durable surface while adding some tooth especially for egg and casein tempera, distemper, encaustic and oil painting. Use in chalk and gesso grounds to increase absorbency and add texture. Bone ash is used in Cennino’s recipe for silverpoint grounds.

Add to oil colors and mediums to create textural and bodying qualities to oil paint without affecting the color. Bone ash has little color in drying oil, so it can be added to oil paint without affecting the color temperature.

 Bone Ash (20 Mesh)Bone Ash (325 Mesh)
DescriptionAsh from calcined and degelatinized boneAsh from calcined and degelatinized bone
Typical Chemical Analysis
Tri-Calcium Phosphate (Ca3 [PO4]O2)95.00%96.90%
Calcium Oxide (CaO)54.50%55.25%
Phosphorus Pentoxide (P2O5)41.50%41.65%
Magnesium Oxide (MgO)<1.25%1.40%
Carbon Dioxide (CO2)0.43%
Silicon Oxide (SiO2)<0.10%0.09%
Iron Oxide (Fe2O3)0.10%0.08%
Aluminum Oxide (AlO)0.06%
Typical Physical Properties
Loss on Ignition @ 1100° C.<0.20%<0.35%
Bulk Density, Loose (kg/L)1.100.80
Specific Gravity (kg/L)3.083.00

How to Use

Put half of the required water together with all the bone ash powder in a container. Add enough water to get a good mixing action. Continue mixing until lump free and uniform consistency is obtained. Do not vortex the mixture in order to avoid air entrainment. Add the remaining water as required by the formula or recipe.

Recipes for Drawing Grounds

The following are instructions from the fourteenth century Medieval painting treatise by Cennino Cennini, Il Libro dell' Arte:

How You Begin Drawing on q Little Panel; And the System for It
Chapter V

As has been said, you begin with drawing. You ought to have the most elementary system, so as to be able to start drawing. First take a little boxwood panel, nine inches wide in each direction; all smooth and clean, that is, washed with clear water; rubbed and smoothed down with cuttle such as the goldsmiths use for casting. And when this little panel is thoroughly dry, take enough bone, ground diligently for two hours, to serve the purpose; and the finer it is, the better. Scrape it up afterward, take it and keep it wrapped up in a paper, dry. And when you need some for priming this little panel, take less than half a bean of this bone, or even less. And stir this bone up with saliva. Spread it all over the little panel with your fingers; and, before it gets dry, hold the little panel in your left hand, and tap over the panel with the finger tip of your right hand until you see that it is quite dry. And it will get coated with bone as evenly in one place as in another.

How to Draw on Several Kinds of Panels
Chapter VI

For that purpose, a little panel of old fig wood is good; and also certain tablets which tradesmen use, which consist of sheep parchment gessoed and coated with white lead in oil,[3] following the treatment with bone according to the system described.

Silver-Point Drawing—What Kind of Bone is Good for Treating Panels
Chapter VII

You must know what bone is good. Take bone from the second joints and wings of fowls, or of a capon, and the older the are the better. Just as you find them under the dining-table, put them in the fire; and when you see that they have turned whiter than ashes, draw them out, and grind them well in the porphyry; and use it as I say above.


3. The Liber illuministarum pro fundamentis auri et coloribus ac consimilibus, Munich, Staatsbibliothek, MS. germ. 821, compiled about 1500 at Tegernsee (Oby.), contains (fol. 33) a rule for these, quoted by Ludwig Rockinger in "Zum baierischen Schriftwesen im Mittelalter," Abhandlungen der historischen Classe der Königlichen bayerischen Akademie der Wissenschaften, XII (1872), 1te Abteilung, p. 18. A translation of this rule follows:

"White parchment tablets are made in this way. Take calf parchment, and put it on the stretcher, and stretch it well; and dry it thoroughly in the sun. And do this thrice. And then take thoroughly powdered white-lead, and mix it with linseed oil until it comes out thin, while still preserving the white color of the white-lead. And paint that calfskin with that liquid color. And then dry it in the sun. And do this nine times; and by all means of the same thickness[?] And one coat is not to be applied unless the previous one be thoroughly dry. This done, you will shape up as many leaves of this calfskin as you wish, and make tablets. And you can write on them with a lead, tin, copper, or silver style, or even with ink, and erase the letters with saliva [not salvia, "sage," as in ed. Rockinger] and write again. And when all the whiteness has disappeared, whiten them again with white-lead and saliva like the ordinary tablets, or with scrapings of shells, bones, or powder of calcined bones, and saliva."

Source: Cennino D' Andrea Cennini, The Craftsman's Handbook. The Italian "Il Libro dell' Arte." Translated by Daniel V. Thompson, Jr. New York: Dover Publications, Inc. 1933.

Other Bone Ash Applications

Bone ash is used in the porcelain industry, especially for the manufacturing of bone china, but due to its outstanding characteristics, it is also most suitable for casting of refined copper, copper alloy and aluminum.

Bone ash in the aluminum industry forms a substantial part of Direct Chill casting of ingots and billets. Bone ash has a direct influence in improving the casting quality, because of the intrinsic benefits described above.

Bone ash can be used as a protective coating on:

• Ladles, launders, troughs, tundishes, etc., made from fused silica
• Ceramic fiber, calcium silicate, castable, etc.
• All metal equipment and tools exposed to molten metal such as metal ladles, sow moulds, ingot moulds, metal troughs, etc.
• Floor areas around mould stations, furnaces and ladles.

More Information
BrandRublev Colours
VendorNatural Pigments
Processing TimeUsually ships the next business day.
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