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Essential Fire Assay Terms

13-Mar-17

TContext03_Cup_Steps.doc

as used in Textbooks

Cupellation Steps: "Driving" - "Freezing" - "Opening" ("uncovering")

Author

Context

Bugbee

When all is ready the buttons are placed carefully in the cupels and the muffle door again closed. If the cupels are thoroughly heated, the lead will melt at once and become covered with a dark scum. If the temperature of the muffle is correct this will disappear in the course of a minute or two when the molten lead will become bright. The assays are then said to have opened up or "uncovered."

This signifies that the lead has begun to oxidize rapidly, raising the temperature of the molten alloy considerably above that of its surroundings, whence it appears bright. It assumes a convex surface, and molten patches of litharge passing down over this surface give it a lustrous appearance. It is then said to "drive." (p. 93)

Bugbee

If the temperature becomes too low for the cupel to absorb the litharge, the crystals begin to form all around and close to the lead in the cupel, and soon a pool of molten litharge is seen forming all around the annular space between the lead and the cupel.

If the temperature of the cupel is not quickly raised, this pool increases in size and soon entirely covers the lead and then solidifies. When this occurs the button is said to have "frozen," although the lead itself may be liquid underneath. Frozen assays should be rejected as the results obtained from them, by again bringing to a driving temperature, are usually low.

If the freezing is noticed at the start, it may be arrested by quickly raising the temperature of the cupel in some way, i. e., by taking away the coolers, closing the door to the muffle, opening the draft, putting a hot piece of coke in front of the cupel, etc. (p. 94)

Bugbee

Keep the door to the muffle closed and when the cupel is red throughout and heated to about 850ºC place the packet of lead and silver carefully in the cupel and close the door to the muffle so that the lead will fuse as quickly as possible.

As soon as the assay begins to "drive," note the time, open the door of the muffle and lower the temperature of the cupel by checking the fire and by placing cold scorifiers, etc., around it. (p. 97)

Bugbee

All assayers agree that the best results are obtained by having a hot start, a cold drive, and a higher heat again at the finish. (p. 98)

Smith

It was found that before "driving" (i.e. rapid oxidation of the lead) commenced, the temperature of the molten lead rose to 900º C or above. (p. 164)

Fulton

If the button weighs from 15 to 20 g, as it should, it will take 25 or 30 minutes to finish the cupellation, that is, to drive off the lead. (p. 34)

Fulton

When the lead button is put into the hot cupel, the lead melts (326º C) and is covered by a gray-black scum. If the lead button is practically pure, as it should be, this black scum disappears when the lead reaches a temperature of 850º C. This is called the "opening up" or "uncovering" of the lead button.

The molten lead then appears bright, begins to "drive," and active and rapid oxidation commences.

Lead buttons should uncover as soon as possible in the muffle. If other and more difficultly fusible metals, such as Cu, Fe, etc., are present, the temperature of uncovering is higher and the temperature required for cupellation is higher. These foreign metals should, however, as a general rule, be absent. (p. 80)

 

 

Cupellation steps: "Blick" - "Blink" - "Brightening" - "Flash" - "Scintillation"

 

Author

Context

Fulton

If now the temperature of the muffle is below that of the melting-point of silver (962º C), or below that of the gold-silver alloy constituting the bead, or if the cupel be withdrawn from the furnace, the "blick" or "brightening" or "flash" of the bead takes place; i.e., the bead suddenly becomes very bright, at the moment of solidification, owing to the release of the latent heat of fusion, which raises the temperature of the bead very much for a short time.

The bead has been in a state of surfusion, i.e., in a state of fusion below its true freezing-point, toward the last of the cupelling operation; and if it be lightly jarred or the temperature allowed to drop still lower (by taking it out of the muffle), it suddenly congeals and assumes a state normal (solid) to the temperature existing. The release of the latent heat, raising the temperature of the bead, causes the brightening.

The "brightening" of very small beads is rarely noticeable. (p. 82)

Fulton

It is an old saying amongst assayers that "a cool drive and a hot blick" are essential to a good cupellation. (p. 86)

Fulton

Beads containing more platinum than 1 in 16 will not blick or flash. (p. 187)

Shepard

If the bead was in a state of surfusion at the finish and consisted of nearly pure gold and silver it would solidify upon further cooling with the emission of a flash of light (known as the "blick" or "flash"). This flash is due to the sudden release of the latent heat of fusion of the alloy at the moment of solidification, which momentarily raises the temperature considerably.

The blick is seldom perceptible in beads larger than 700 mg. Small amounts of lead or copper in the bead diminish the intensity of the blick.

All the platinum group of metals, with the exception of platinum and palladium, suppress the blick entirely. If the blick is observable, it is a useful guide to the completion of cupellation, but the assayer need not waste time trying to observe the blick, as the end of cupellation is easily ascertained by other observations. (p. 63)

Smith

If the cupel is withdrawn from the furnace, the button becomes very bright at the moment of solidification and is said to "flash", "brighten" or "blick". This "flashing" of the buttons of gold or silver is due to the evolution of the latent heat of fusion or "recalescence", which momentarily reheats the cooling globule to its melting-point.

The flashing is much more noticeable with gold than with silver buttons. Molten gold has a peculiar green colour which is easy to recognise and just after solidifying it glows beautifully, even with very small buttons. With very small silver buttons the flashing is rarely noticeable.

The flashing is prevented if the buttons contain metals of the platinum group. (p. 160)

Smith

Kühl getrieben, heißer Blick, ist des Probierers Meisterstück (p.161)

Probierbuch

Kalt getrieben und heiss geblick ist im probiren ein Meisterstück

Cool at driving, hot at 'blick', this is the assayer's master trick.

Neuss

Kalt getrieben und heiss Blick ist der Probierer Meisterstück

 

 

 

 

 

English

Deutsch

Nederlans

Français

Italiano

Castellano

Русский

assay ton

Assay ton

assay ton

assay ton

assay ton

assay ton

пробирная тонна

blank test

leere Probe

leeg proef

essai en blanc

prova in bianco

prueba en blanco

холостая проба

blick / blink
scintillation

Silberblick

flonkering

étincellement
(de l'argent)

scintillio
(dell'argento)

centelleo
(de la plata)

мерцание - сцинтилляция

driving, drive

treiben, getrieben

sturen

 

 

tracción

 

feathers (litharge)

Feder (Bleioxid)

veer (litharge)

plumes (litharge)

penne (litargirio)

plumas (litargirio)

перья (окись свинца)

freezing

Einfrieren,
Erstarrung

invriezen

congélation, solidification

congelamento /
solidificazione

congelación / solidificación

конгеляция,
затвердевание

matte, regulus

Matte, Stein, Lech

matte

matte

matte

mata

штейн

opening, uncovering

Öffnung

openen

amorce

apertura

destape

открытие

play of colours

Farbenspiel /
Schillern

kleurenspel

éclat multicolore /
irisation

iridescenza

iridiscencia

Иризация

spitting

Herausspritzen

spatten

éclabousser

spruzzare

salpicar

отхаркивание

sprouting, vegetation

sprießen

spruitje, /
scheut

arborescence

arborescenza

arborescencia /
brote

Проращивание

speiss

Speise

speiss

speiss

speiss

speiss

шпейз

surcharge

Zuschlag /

Überlastung

overgewicht

surcharge

sovraccarico

sobrecarga

перегрузка

 

 

 

 

 

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Fire Assay

Bibliography:

Textbooks

 

 free download from

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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