How to Assay Gold
Prepare your equipment., Place the sample in a crucible., Combine any additives., Heat the reaction to completion., Pour off the top layer., Cool the metal., Cupel the metal., Dissolve the silver., Wash the gold., Weigh the gold.
Step-by-Step Guide
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Step 1: Prepare your equipment.
You will need a crucible to put the sample into.
You will need a heat source such as a torch or furnace to bring the sample to high temperatures.
You will also need other reactants such as the additives to create the flux, the bone ash to cupel the metal, and some sodium nitrate to extract residual silver.
You will also need molds to pour hot metal into.
Also wear goggles, heat resistant gloves, and ideally a fireproof suit. -
Step 2: Place the sample in a crucible.
The crucible needs to be able to withstand high temperatures.
The sample will be exposed to enough heat to melt all of the metals and separate them from other minerals.
Clay or ceramic crucibles can withstand tremendous heat., Additives such as lead oxide, sodium bicarbonate, potassium carbonate, and flour are used to form a flux.
The flux reacts with the same (or ore) to promote melting.
Different ratios of each additive will produce slightly different flux compounds., The flux reaction needs to be heated to completion.
When the reaction is complete, you will see two separate layers.
Depending on the laboratory and the additives used, you will typically heat to between 1,100 and 1,200 degrees Celsius (2,012
- 2,192 degrees Fahrenheit).
The top layer is molten glass that contains no valuable minerals.
The bottom layer contains your molten precious metals., Carefully discard the top layer of molten glass.
It will be of no further use in the assay.
No gold, silver, or other metal will be lost by doing this.Be careful not to pour off any of the metal layer. , Pour the metal into a mold.
In the mold, the metal can cool until it once again reaches a solid state.
This metal is now comprised of gold, silver, and lead.Be very careful, as the metal will be hot for a long period of time and can severely burn you. , A cupel is a porous container made of bone ash that will readily absorb lead oxide.
To cupel the metal, you place it in the cupel and blast it with hot air.
This will oxidize the lead.
The lead oxide will then vaporize or be absorbed by the bone ash.
After cupling, you will have a metal sample that is composed of gold and silver., Submerge the metal in nitric acid.
The acid will not dissolve the gold, but it will dissolve the silver.
You can then pour the solution through a filter to separate the gold., Wash the gold with water to remove any excess nitric acid.
Pat the gold dry with a soft towel.
At this point, you should have a sample that is nearly pure gold., With all contaminants removed, you can weigh your gold on a scale.
By comparing the weight of the gold to the weight of the original sample, you can determine the percent weight of gold in your ore or scrap.
This completes the fire assay of the gold piece. -
Step 3: Combine any additives.
-
Step 4: Heat the reaction to completion.
-
Step 5: Pour off the top layer.
-
Step 6: Cool the metal.
-
Step 7: Cupel the metal.
-
Step 8: Dissolve the silver.
-
Step 9: Wash the gold.
-
Step 10: Weigh the gold.
Detailed Guide
You will need a crucible to put the sample into.
You will need a heat source such as a torch or furnace to bring the sample to high temperatures.
You will also need other reactants such as the additives to create the flux, the bone ash to cupel the metal, and some sodium nitrate to extract residual silver.
You will also need molds to pour hot metal into.
Also wear goggles, heat resistant gloves, and ideally a fireproof suit.
The crucible needs to be able to withstand high temperatures.
The sample will be exposed to enough heat to melt all of the metals and separate them from other minerals.
Clay or ceramic crucibles can withstand tremendous heat., Additives such as lead oxide, sodium bicarbonate, potassium carbonate, and flour are used to form a flux.
The flux reacts with the same (or ore) to promote melting.
Different ratios of each additive will produce slightly different flux compounds., The flux reaction needs to be heated to completion.
When the reaction is complete, you will see two separate layers.
Depending on the laboratory and the additives used, you will typically heat to between 1,100 and 1,200 degrees Celsius (2,012
- 2,192 degrees Fahrenheit).
The top layer is molten glass that contains no valuable minerals.
The bottom layer contains your molten precious metals., Carefully discard the top layer of molten glass.
It will be of no further use in the assay.
No gold, silver, or other metal will be lost by doing this.Be careful not to pour off any of the metal layer. , Pour the metal into a mold.
In the mold, the metal can cool until it once again reaches a solid state.
This metal is now comprised of gold, silver, and lead.Be very careful, as the metal will be hot for a long period of time and can severely burn you. , A cupel is a porous container made of bone ash that will readily absorb lead oxide.
To cupel the metal, you place it in the cupel and blast it with hot air.
This will oxidize the lead.
The lead oxide will then vaporize or be absorbed by the bone ash.
After cupling, you will have a metal sample that is composed of gold and silver., Submerge the metal in nitric acid.
The acid will not dissolve the gold, but it will dissolve the silver.
You can then pour the solution through a filter to separate the gold., Wash the gold with water to remove any excess nitric acid.
Pat the gold dry with a soft towel.
At this point, you should have a sample that is nearly pure gold., With all contaminants removed, you can weigh your gold on a scale.
By comparing the weight of the gold to the weight of the original sample, you can determine the percent weight of gold in your ore or scrap.
This completes the fire assay of the gold piece.
About the Author
Douglas Davis
Committed to making hobbies accessible and understandable for everyone.
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