Page 6
5 ◄  Page  ► 7

Essential Fire Assay Terms

13-Mar-17

TContext06_Play_Colours.doc

as used in Textbooks

"Play of Colours""Brightening"

Author

Context

Shepard

The visual phenomena that appear near, and at the finish of cupellation are of considerable aid to the assayer.

Since both silver and gold have a higher surface tension than lead the button becomes more rounded as the percentage of lead decreases; this effect becomes pronounced as the proportion of precious metals increases beyond 50%.

When the cupellation of large beads approaches completion, oily-appearing drops of litharge can be seen to collect on the surface of the bead. These particles appear to move, and the movement becomes increasingly more rapid until just before the finish, when the molten litharge forms a thin film of variable thickness and creates interference colors.

The rainbow color bands move swiftly over the surface of the button and give the illusion that the button is revolving about a shifting axis. This is known as the "play of colors" and is strikingly developed with large beads.

When the last trace of lead has been removed from the bead the play of colors disappears and the bead becomes dull for a brief period, after which it acquires a normal metallic luster. This change of luster is known as "brightening" and is not always observable. (p. 62)

Fulton

... just as the last of the lead oxidizes (play of colors). (p. 95)

Beringer

The drops of litharge which in the earlier stages flow steadily from the surface of the alloy, thin off later to a luminous film.

At the end this film appears in commotion, then presents a brilliant play of colours, and, with a sudden extinction, the operation is finished.

The metal again glows for an instant whilst becoming solid.

 

 

English

Deutsch

Nederlans

Français

Italiano

Castellano

Русский

 

 

 

 

 

 

 

play of colours

Farbenspiel /
Schillern

kleurenspel

éclat multicolore /
irisation

iridescenza

iridiscencia

Иризация

 

 

Sections

Icons

Details

Links

Fire Assay

Bibliography:

Textbooks

 

 free download from

► Internet Archive

► I. A.

REFERENCE BOOKS
"A Textbook on Fire Assay"                                                                Edward E. Bugbee
"Fire Assaying"                                            Orson C. Shepard & Waldemar F. Dietrich
"A Manual on Fire Assaying"                                                       Charles Herman Fulton
"The Sampling and Assay of the Precious Metals"                            Ernest Alfred Smith
"Metallurgy of Gold"                                                                                 Thomas K. Rose
"The Precious Metals
: comprising Gold, Silver and Platinum"               Thomas K. Rose
"A Text Book of Assaying"                                                   C. Beringer & J. J. Beringer


Bugbee
Shepard
Fulton
Smith
Rose1
Rose2
Beringer

 

 

Context: ►Assay Ton  ►Blank  ►Steps   ►Feathers  ►Matte/Speiss  ►Colours  ►Spitting  ►Sprout  ►Surcharge  ►Inquart  Hallmark  ►Cupels

Terms: ►Cupellation  ►Fire Assay  ►Reagents  ►Other Methods  ►Metals Sheets: ►Cupels  ►Crucibles  Index: ►Programme