Butler Lab

Torch Fire Assaying for Noble Metals

My Grandfather

Charles L. Butler


Welcome to Butler Lab's
Torch Fire Assaying
Information Page

We, here at Butler Lab, have developed an assay procedure to be used as a supplement to furnace assaying of the noble metal ores. It is quick and inexpensive, with most assays requiring 15 to 20 minutes and costing something less than 50 each. Since these tests may be performed equally well at home, in the field or laboratory, this procedure becomes very useful to the novice and professional, alike. Most Clients learn the procedure within 10 to 12 hours.

Torch Fire Assaying

 We find it an excellent prospect tool and field guide for the drilling crews. It can also be used to assay mill run samples and tails, leach solutions, chemical precipitates and any of the noble metallic salts, including silver, gold and the platinum group metals. It is ideal for assaying wet or dry concentrates from one's recovery system and the flow water being used in said system. This water, when working with ores carrying water soluble values, will carry away a portion of one's values unless steps are taken to save them.

One can equip his lab for about $450.00 to perform Torch Assays. The oxy-acetylene torch, tanks and regulators are the one big expense. The infinite number of possible torch flame settings allows one to create the reductive or oxidizing flames when they are required. As a result, only two fluxes are required and we seldom have a failure. When difficulties do arise, we are made aware of it within a minute or so, allowing the assayer a chance to make any needed adjustments of the torch, or the addition of either type flux.

Gold Ore

When assaying for the "noble metals", in order to free our metallic values, one must create a liquid fusion of the "assay charge". We do this by mixing our crushed sample with the proper assay flux and placing same inside a charcoal crucible. Then, with our oxy-acetylene torch adjusted to the proper oxygen to acetylene ratio, we create the "reductive flame" required to liquefy the assay. The intense heat from the torch, applied directly down over the assay, creates temperatures in excess of 2,000 degrees centigrade, enabling one to recover all of the noble metals, if present.

Secondly, one needs a "collector" to collect and hold any liquefied gold, silver or platinum group values the tested sample may have contained. We accomplish this with one of our flux ingredients, "litharge" a lead oxide powder. When performing correctly, heat from our reductive torch flame changes this litharge to liquefied lead. This lead alloys, or combines with all the molten noble metals, except osmium, one of the platinum group. When assaying specifically for the platinum metals, most assayers add a silver "inquart", either as foil or wire, to act as their collector, as silver does alloy with all platinum group metals. In addition, the extreme effects the PGM's have on the silver "beads", makes for easy recognition that platinum metals are present.

Thirdly, the fusion procedure must produce a 1/8 to 5/32 inch diameter lead "button". This lead will start to appear as real small, shiny beads, within the first 30 to 40 seconds, after applying the reductive torch flame to the assay charge, if everything is working as planned. Failure to observe any tiny lead beads, indicates "trouble". A few difficult ores do require the adding of a second measure of assay flux. When fusion is complete (everything liquefied) and all lead has settled to the bottom of the crucible, we dump the "slag", leaving the lead button in the crucible for "scorification".

Our fourth step is the scorifying of the lead button to remove any "base metals" (metals other than noble metals) that were picked up by the molten lead. This is performed by adding a small pinch of borax glass, then applying a highly oxidizing torch flame. The lead button will catch on fire, burning at over 3,000 degrees centigrade. This high heat changes all base metals to "scoria" or ash, which joins the molten borax glass as a slag, for disposal. The somewhat smaller lead button, containing any noble metal values that were present, is dumped out onto an aluminum plate for cooling.

Our next step is to "cupel" the button, to dispose of the lead. Our cupels are small, bone ash cups. Their porosity adsorbs the liquid litharge, created by the oxidizing of the lead button, with the oxidizing torch flame. Cupelling is complete, when the button, growing smaller, becomes a bead, refusing to reduce in size any further. After the torch is withdrawn, most beads will "blick", or flash, just as they begin to cool, at the very instant they change from liquid to a solid. These beads are referred to as "dori beads", as they may contain any or all of the noble metals, silver, gold, platinum, palladium, iridium, osmium, rhodium and ruthenium. The assayer must determine which, with additional testing.

All measurements and computations are based on the volumetric principal, instead of by weight. This, since scales sufficiently accurate for this work would be very expensive and inappropriate for outdoor use. A small, accurately calibrated spoon is used to measure out the material to be tested. A spoon five times larger, is used for measuring the flux. The noble metals are recovered as a small, round bead, its diameter is measured with an inexpensive 40X power, optical comparator, rather than weigh them, to determine the value of the ore which produced them. Through measurement and the use of our "discoloring solution", most ores can be evaluated. However, some beads do require "parting", with nitric acid and distilled water to remove the silver, then rebeaded, before their ore can be evaluated. Our discoloring procedure lets us know when parting is necessary. Actually, parting is seldom required, as at least 90% of one's tests can be evaluated through use of natural observation and our "Bead Discoloring Procedure". It readily identifies all beads containing 75%, or more, silver and lets us know the approximate silver content, ranging from 75% to 100%. The results are expressed in "Troy Ounces" of silver or gold and platinum group metals per ton of materials being assayed.

It is absolutely essential that these tests be performed in a well ventilated area, since the flux contains toxic compounds, as do some ores. Breathing or ingesting these materials as powder or fumes, can be hazardous to one's health. Eye protection is also required when using the torch.

Gold Bead

The following facts, comparing our procedure with the conventional, furnace fire assay, will further indicate the different ways in which we have advanced the art for the prospector and miner.

l. There is no massive furnace to be heated, only a small assay weighing a few grams and a two ounce crucible.

2. The "fusion charge", in the conventional assay, just lays there, within the crucible, without benefit of any appreciable mechanical stirring to assure that the molten lead will come into contact with the entire melt, during fusion. In our method, the crucible is manually rocked around in a circular motion, and in addition, the flame is used to stir the melt, assuring complete alloying of the lead and any noble metals contained within.

3. Our method eliminates removal of any tiny beads from the cupels, cleaning and weighing them, tedious task, at best.

4. The entire process is carried out under one's visual observation, from start to finish. This allows for the immediate adjustment, if necessary to correct for conditions caused by some troublesome ores.

5. The light weight, mobile equipment can be taken anywhere in the field, by providing a temporary windbreak to work behind.

6. With the Torch Assay Procedure, one can develop, prove and promote his gold, silver or platinum mine, right there on site.

7. People, who continue to perform furnace assays, may wish to learn torch scorifying and cupelling, especially if their ore contains one or more of the troublesome metals, such as nickel or copper.

8. Probably, the most important feature of all, is the fact that one receives an answer within minutes, instead of hours, days, or weeks.

9. Hundreds of clients have learned to assay and leach their noble metal ores, through use of our step by step, instruction manuals, listing all required supplies and their source.

10. Following items mailed postpaid, by Priority Mail.


Oxyacetylene Torch Assaying...............By Charles L. Butler.....................................$50.00
Leaching With Safe Chemicals..............By Charles L. Butler.....................................$50.00
Set of 2 Duke's Mineral Manuals.............By Raymond Maulsby.................................$60.00
Two Hour,VHS or DVD, Assay & Leaching Video...........Close Up Views...............$100.00
Four Hour, One on One, Assay Lesson, at our Lab..................................................$200.00


Chemicals & Supplies Available - - - Ask for Brochures & Price List

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Butler Labs
6025 Cocktail dr.
Las Vegas, Nv 89130

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