Fire assay magnesia ash dish

ASHES ASSAY CRUCIBLES

Ashes assaycruciblesare specially suitable to work with scraps & residues. 

In addition, our ashes assay crucibles have a pronouced inner conical shape to optimize the separation of the lead and slag phase. This is particulary useful if the ashes assay crucibles is only fired one time. The reason is that this avoids the use of a lead button conical mould.

Ref	SHSC65	SHSC60	SHSC80S	SHSC80	SHSC80T
Dimensions in mm: Ø – Upper External  Height	65 68	60 108	80 130	80 150	80 180
Volume (ml) Weight (g)	90 210	110 200	260 380	300 480	430 620

Reference	Diameter mm	Height mm	Volume ml
SC50	50	25	15
SC65	65	25	23
SC80	80	28	45
SC100	100	37	70

FIRE ASSAY METHOD
Since many centuries, Fire Assay is the traditional method to determine the metal contents of a sample. Typically, this sample is an ore or some kind of residue with some precious metal contents (Gold, silver and platinum group Metals). Although the method is very old, it is highly accurate and widely used.
The principle of Fire Assay is to separate the metals from the other components of the sample. At the end of the process we weight the separated metals in order to determine the amount of precious metals present in the original sample.
It is possible to complete the Fire Assay process, whether with a reductive fusion with Fire Assay Crucibles, or with an oxidative fusion using Fire Assay Scorifiers.
To separate the metals, it is necessary to first mix the sample with fluxes such as:
ComponentEffect
BoraxReduce melting point
Soda (Sodium Carbonate)Desulfurization
SilicaReduce melting point
LithargeOxidization
 
 
FIRE ASSAY PROCESS with FIRE ASSAY CRUCIBLES
The first step of the process consists of mixing the samples with the above fluxes (and or others). Then we place the mixture in Fire Assay Crucibles (or Ashes Assay Crucibles) for fusion at 1250?C. Under these conditions and with these fluxes, a reduction of the metal oxides present in the sample takes place. The litharge added at the beginning reduces also into lead and acts as a “solvent” for the metals. This lead rains down / precipitates at the bottom of the fire assay crucibles and forms a metallic lead phase. On top of the lead, there is a slag phase. We have therefore two phases:
One heavy lead metallic phase at the bottom of the crucible. If the fire assay proces is conducted properly, this phase contains all of the precious metals.
A lighter slag phase at the top of the crucible. Slags are mainly silicates.
 
Separation of the lead phase from the slag
At this point there are two possibilies.
If we know or suspect that the sample contains precious metals then we just leave the fire assay crucibles to cool. Once cold enough, and the two phases have solidified, we break the fire assay crucibles and separate the metallic lead button phase for further analysis (typically cupellation).
On the other hand, if we suspect that the sample is not likely to contain any precious metal then we pour the the contents of the fire assay crucibles into a conic mould and let the lead solidify in it.