How many of you are assaying?

I downloaded Smith's assaying book and read most of it. He seemed to ramble a bit, and 3/4 of the way through the book still hasn't explained the chemistry of assaying. :lol: But I'll get there.

Most of what he describes, though, is assaying ore. And he's looking for very small concentration of gold in that dirt / rock.

How many of you are assaying with scrap gold? Say, 50% gold?

Are any of you assaying >98% gold? Is assaying accurate at those concentrations?

i thought the whole purpose of assaying was to find the percentage of all metals in a given sample.

Sorry if I wasn't clear.

I was wondering how many of you were performing assays. And if you were, did you generally concentrate on assaying fine gold, or gold in concentrations found in scrap gold, or even assaying ore material.

Run about 20 gold samples per day. About half are fire assays where the sample ranges from 2-99% gold. Back in the late eighties used to do about 10 ore assays a day.

The balance is refined gold (99.95 - 99.999%) which is assayed via an ICP spectrometer. The trace impurities are totaled and subtracted from 100% to come up with the gold percentage.

Sorry, do not do assays for the public. Maybe someday I will start my own assay lab, but time is running out on that dream.

Is there a particular reason why you wouldn't use the ICP for general assays? (FWIW, I ran an Atomic Absorption unit for a little while early in my career). It seems curious that you save the ICP for fine gold.

Perhaps to confirm Good Delivery Bar, ICP is needed?

There are people that use ICP to determine gold content in less than pure materials, alloys and such.

It is my experience that ICP is very well suited for trace amounts of contaminants and not so much for alloy constituents. Gold and silver in the 10-99% range I feel is much better done via fire assay for gold and either fire assay or silver chloride precipitation for silver.

We do use ICP for samples where gold is <0.1%, anything higher than that we use fire assay.

It's just a ball park guess, but I have probably run at least 10,000 fire assays in my life - most recently, about a year ago. About 3/4 of these were on electronic components, many of which ran less than 0.1% gold (about $25/pound). In isolated cases, I have used other methods for electronic components but I feel that, in general, fire assay is the most reliable.

I used to do assays about 30 years ago :lol:


With scrap gold it is a different procedure without all of the fluxes of an ore sample.

You start with .1 gram samples weighed on an analytical balance for assay.
You will need an analytical balance or your wasting time trying to get an accurate assay.
.ooo1 gram accuracy is suggested
The assay balance needed is glass inclosed and needs to sit on an antivibration balance table.
.5 grams of gold free silver is weighed to add to each sample, (inquarting)
Samples and silver are wrapped in assay lead foil
Bone ash cupels are pre heated for 10 minutes
Samples are placed in cupels
cuppellation is complete in about 10 minutes
Some of the lead is absorbed into the bone ash and the remainder volatillizes.
The resulting beads are cleaned of bone ash and hammered or rolled flat and parted in
20% hot nitric acid and distilled water
then rinsed after the reaction stops.
After the reaction stops , fresh 20% nitric acid is added and brought to a boil.
Then the residue is rinsed with distilled water 5 to 10 times.
Then dry to a constant weight at 110°C and anneal.
You then brush the dried and annealed residue onto your balance watchglass and weigh.
Then weigh the remaining residue and calculate your %
The % result is your gold percentage of your sample.

If your weight was .1 gram and your result weight is .075
so your sample is 18K gold 18k divided 24k = .75

If your sample is .2 and your result is .1167 then
your sample is 14K

That's a good point about assaying for all metals
But the analysis for metals other than gold or silver
can be accomplished with gravimetric analysis or plasma spectrometry or X-Ray analysis.
That's out of my league but they did it at one of the refineries that I worked at in Hayward.

Back at our refinery, we didn't receive scrap or bullion with pgm's very often so we seldom assayed for anything
other than gold and silver.

Of course if the scrap or bullion is thought to contain platinum groups then you would assay for those also.