Comment

Comment by Norm Stuart on April 13, 2014 at 11:23am

Thank you.  I can see I will be learning quite a lot from you.

Comment by Daniel Spruyt on April 13, 2014 at 1:35am

See also my presentation on Chemistry in Ceramics (Too big to attach here)

See my website:

Chemistry in Ceramics

Comment by Daniel Spruyt on April 13, 2014 at 1:22am

Hi Norm,

There is one place where the metal ion can bind: on the only carboxylic acid function.

I attach here a picture. If interest for chemistry in ceramics, I will put my complete PowerPoint presentation I made for lectures I gave. It will be on a separate discussion item.

Comment by Norm Stuart on April 12, 2014 at 10:04pm

Do you know what portion of the Abietic Acid molecule the metal ions bind to?

Comment by Daniel Spruyt on April 12, 2014 at 5:21pm

The basic mechanism is that metals are bound to a large organic molecule. Most often Abietic acid, the major component of pine rosin. Being metal salts of abietic acid, during combustion the excess of carbon from the abietic acid  reduces the metal back to its native state.

Comment by Norm Stuart on April 12, 2014 at 1:57pm

Thanks.  "Bright Gold" products contain a lower percentage of gold, typically 12%, than "Premium Gold" products which have more like 18%. But "Bright Gold" has a lighter and brighter luster. Duncan in the US, and other suppliers around the world, repackage luster products manufactured by Johnson Matthey.  In fact Johnson Matthey offer a larger variety of product ranging between their Bright and Premium products.

http://www.colour.matthey.com/precious-metals/brushing

Johnson Matthey bonds gold or platinum acids to sulfonated oils.  An oil like Caster or Laurel oil bubbled with hydrogen sulfide so a sulfur molecule has taken the place of a carbon at one end of the molecule.  Metal ions, added as a metal acid, readily bond to the sulfur atom on the oil.  This is often called Red Turkey Oil.  Making a high yield of metal bonded red turkey oil is extremely difficult requiring exacting reaction temperatures.

Red turkey oil bonded to a variety of other metals is also added - typically Rhodium, Bismuth, and Antimony along with coloring metals like Cobalt, Copper, and others.  The mixed red turkey oil with metal ions attached is made more liquid with Toluene.  The horrible smelling Toluene evaporates while it is applied to the ware.  In the kiln the red turkey oil and any remaining toluene burns off leaving the metal ions attached to the aluminum silicate ceramic. 

The Bismuth and Antimony provide their ability to bond with aluminum silicate ceramic just as well as they bond to gold or platinum - so they're the glue which attaches the precious metals.  The Rhodium prevents the gold or platinum from forming large crystalline structures, rather than a thin uniform layer on the surface.

In reading about this material is industry journals, I've learned that much of the chemistry of metallic lusters is still not fully understood.

Comment by Daniel Spruyt on April 12, 2014 at 11:38am

It is not Duncan Premium Gold as far as I know. It is sold by my Belgian supplier under its own name as (translated) Bright shiny Gold.

Comment by Shine Chisholm on April 12, 2014 at 11:25am

Ah. Sorry. Thanks for the clarification.

Comment by Norm Stuart on April 12, 2014 at 11:19am

Duncan Premium Gold?

Comment by Daniel Spruyt on April 12, 2014 at 10:52am

I have to stress that it is not a glaze but a luster: fired at 750°C as a third firing over a C6 glaze.

Thanks for the comment.

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