Equipment Used For Firing/Smelting Ore
Furnace Or Oven For Firing/Smelting: It must heat to 1950 degrees F for gold and 2100 degrees F for silver. A muffle furnace is best. It fires to about 2300 degrees F and the ingredients can be easily added to the ore while firing.
Crucible: Clay or graphite crucible to use in a muffle furnace. Other types of crucible can be used in an electric furnace.
Stirring Rod: A ¼ -inch diameter steel rod about 3 feet long works very good. Welding rod doesn’t hold under high temperature.
Tongs: Long-handled tongs to remove crucible from furnace.
Hammer: A hammer to break up the slag after it is completely cool.
Mortar And Pestle: You can use a 4-inch diameter pipe cap as a mortar and a piece of pipe 8-10 inches long with pipe caps on both ends as a pestle to crush the ore. A small strainer or screen to take out the bigger pieces of ore for finer crushing is often useful. You can pour slag into a mortar or pipe cap when it is hot from the furnace. When the metal has cooled, you can use the pestle for breaking out the button of metal.
Angle Iron: To add necessary ingredients while the ore is in the furnace, a 3-foot piece of 1-1/2 inch angle iron is handy.
Ingredients For Firing And What They Do
Wheat Flour And Hydroquinone: Makes carbon and adds heat from the inside to give the metal its identify.
Sand: Added to the bottom of the crucible to keep the ore from sticking and added to the top of the metal so that it will not volatilize. When the metal is in liquid form, it volatilizes the same way water will steam when it boils.
Oil Or Lard: Used to help the ore form together into a button or ore bar. It also helps to build up heat.
Soda Ash: Used to thin down slag, cover and clean metals.
Potash Or Lye: Thins slag from gold and helps in cleaning.
Borax: Used to cover and clean gold. It also helps to keep the gold from volatilizing off.
Crushed Ore: The ore needs to be crushed so that it can heat and fire down faster.
The Dangers Of Firing Ore
Fumes from many ores can kill. Make sure you have adequate ventilation when firing any ore. Normally, a good vent hood and exhaust fan are sufficient.
Never fire any ore that contains mercury or cinnabar without excellent ventilation, as mercury volatilization off at a very low heat and produces a very deadly gas.
When pouring molten ore, make sure the container that you are pouring into is absolutely dry and free from moisture. Trapped moisture will explode into steam.
A muffle furnace is probably the best source of heat for firing ores. It’s a good idea to have a piece of paper burning in the furnace before turning on the page.
Fluxing And Firing/Smelting Silver Ore
- Un-iodized table salt
- 1 cup crushed ore
- 3 tablespoons soda ash
- 1 tablespoon wheat flour
- 1 teaspoon lard or oil
- ¼ cup silicon sand
- 2 tablespoons borax
- Furnace or oven
- Mortar and pestle
- Stirring rod
- Angle iron
- Long-handled tongs
- 2 cup crucible
Steps For Firing/Smelting
- Mix the ore, wheat flour lard and ½ of the soda ash.
- Put ½ of the silicon sand in the bottom of the crucible and add the ore mixture.
- Cover the ore mixture with the remaining soda ash, the borax and the silicon sand.
- Place in the furnace and put on high heat (2100 degree F). It takes about 2 hours or longer, so don’t get in a rush. The ore should go thin and look like honey. There will be spots of fire or black spots at first. These are the wheat flour and carbon making the metal take on its identify. If the ore is too thick, use potash to thin it. Keep adding slowly, a bit time, until the ore thins to the consistency of honey. If it starts to boil over, add some salt, however, makes sure it keeps boiling. When the ore looks like honey and lays flat, it is ready to pour. Make sure there are no lumps in it.
- Lift the crucible out of the furnace with the tongs.
- Rotate the crucible 3 or 4 times and then pour it quickly into a dry mortar.
- Let it cool. You should have a slag that looks like colored glass with a metal button on it.
- Remove the button with a hammer or pestle. To make sure you have all the metal, pan the slag. Sometimes the slag will need to be fired more than once. Repeat the process.
- Put the button through nitric acid or aqua-regia to find out what metals it contains and how much there is.