FreeShip- Bone Ash, Translucent for Bone China - (Prompt rebate on orders with 3 or more FreeShip items!)

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Bone ash has been used in ceramic bodies for over 200 years primarily to make bone china. They even know the specific year and person who "invented" bone china, Thomas Frye at the Bow porcelain factory in 1748. Large percentages of bone ash added to porcelain bodies results in high translucency, but has been known to be difficult to produce. It's made like it's name implies, by calcining bone (usually cattle bone). Calcining clay drives off both the free water at around 420 F and the chemically bound water between 650 F and 1300 F (different sources give different ranges; I've seen 900-1300 F, 660-1470 F, and others; most often the 1300F figure is given as a safe upper temperature for when the "bound" water is gone). Is calcining materials other than clay done at the same temperatures? No. They calcine bone at about 2010 F to make bone ash.
These days you may be getting a synthetic alternative, tricalcium phosphate, when you buy bone ash. They should list that after the "Bone Ash" label.
It does have other uses in the arts. CAMEO, the art material database states { http://cameo.mfa.org/wiki/Bone_ash }:
"A white powdery material made by calcining bones, usually from cattle. Bone ash primarily contains calcium hydroxyapatite with small amounts of magnesium phosphate, calcium carbonate, and calcium fluoride. It is used as a polishing agent and as a flux in ceramics. Bone china can contain 25-50% bone ash. Bone ash has also been used as a pigment called bone white in grounds for silver point drawings."
And here { http://cameo.mfa.org/wiki/Bone_white } : "An obsolete white pigment made from bone ash. Bone white was primarily composed of calcium hydroxyapatite and calcium carbonate. It was used in grounds for silver point drawings, in making ceramics and as a polishing compound."
The pigment "bone white" is considered a "historical" pigment, now rarely used and without a Color Index Name.
It's listed at the top of the heap of historical pigments in the very comprehensive "Art Is Creation" database, in the "The Color of Art: Pigment White, PW" section { http://old.artiscreation.com/white.html }.

The supplier says: "An important source of phosphate in ceramic glazes. When added to a clay body such as bone china, it lowers the maturing temperature and adds translucency. Also used to give texture to low fire ceramic glazes."
Digital Fire, the ceramics database states { https://digitalfire.com/4sight/material/bone_ash_123.html } :
"Real bone ash is obtained by calcining bone up to approximately 1100°C and then cooling and milling. This material is still manufactured today since some of its important properties are due to the unique cellular structure of bones that is preserved through calcination. Real bone ash has excellent non-wetting properties, it is chemically inert and free of organic matters and has very high heat transfer resistance.
Bone ash has traditionally been added to porcelain to achieve a high degree of translucency (thus the name 'bone china'). The manufacture of bone china is difficult to master because the clays are non-plastic, ware is unstable in the kiln, and it is difficult to burn consistently to the body's narrow firing range. Today the availability of super-white kaolins, low iron feldspars and processed bentonites, smectites and hectorites makes it possible for almost anyone to make very white, translucent and strong porcelains even at cone 6.
Bone ash is not common in glazes. When employed it can cause the slurry to flocculate and thicken (and produce a very thick layer on the ware surface which cracks during drying). People often react to this by adding more water, producing a glaze that shrinks even more on drying and eventually thickens again. A better way is to add a little deflocculant to the glaze slurry (like Darvan).
Up to 1-2% bone ash can be used in enamels for opacification (more will usually cause pinholes). In glazes, as with enamels, too much or too high a temperature will cause blistering. In this use the phosphorus' influence toward a stiff melt generally checks the fluxing action of the calcia.
Bone ash or calcium phosphate are used to opacify opal glass (1-3%) because the P2O5 content forms colorless compounds with iron impurities."
Bone ash is also a glaze opacifier and gives texture to a glaze. If too much is added crazing or blistering will result.

Wikipedia adds some info about it's production and use in bone china { https://en.wikipedia.org/wiki/Feldspar } :
"The raw material for bone china is about 50% bone ash derived from animal bones. These bones undergo multiple processing stages during which all meat is removed and the bone is completely cleaned. Once cleaned, the bone is heated to about 1000 °C (1832 °F) so that all additional organic material is removed from the bone and the bone becomes sterilized. Lastly, the newly sterilized bone is ground with water into fine particles which can be used as a raw material for bone china. Bone ash plays an important role in the creation of bone china, as the phosphate of the bone generates beta tricalcium phosphate, and other compounds from the bone create a calcium crystal called anorthite. Synthetic alternatives dicalcium phosphate and tricalcium phosphate are used as substitutes for bone ash. Most bone china are produced with synthetic alternatives rather than bone ash."

Wikipedia lists another highly interesting use for bone ash that I had never heard of, as a coating for metal in machining (if I was still machining I'd try it): "Bone as is used in machine shops for various purposes. Examples include polishing compounds, protective powder coatings for metal tools......As a powder coating, bone ash has many unique characteristics. First of all, the powder has high thermal stability, so it maintains its form in extremely high temperatures. The powder coating itself adheres to metal well and does not drip, run, cause much corrosion, or create noticeable streaks. Using the bone ash is easy as well, as it comes in a powder form, is easy to clean up, and does not separate into smaller parts (therefore requiring no extra mixing).-

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Reviews

Reviews (9)

Average:

May 25, 2024

Quick shipping, good communication, and arrived safely.

Dylan Smith

Dec 1, 2022

Megan

Oct 19, 2022

Tony

Jun 26, 2022

Exactly what I needed. Arrived quickly. Well packaged. Seller prompt to send shipping updates. Thank you greatly.

Sethaka

Jun 4, 2022

Beautiful and unique art materials

Angel Ramos