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How to Estimate Gold Content in Gold Plated Parts

When trading electronic scrap or jewelry, we sometimes have to quote plated materials.

When the material is homogenic, we can estimate the gold content  in 3 main ways:

  1. The most accurate way is taking a sample, dissolving the gold in a solution, precipitating it and

then casting the precipitated gold. This is actually a refining process (which is more complicated and

not suitable for everyone). You can learn more in this video.

  1. In case the plated materials are brass or copper it is possible to cast a sample and analyze it with “Fire Assay” or XRF to identify the gold content.
  1. A less accurate but quick method, is estimation of gold content by the thickness of the gold-plated parts. This method is limited in its accuracy due to non-homogenous coating layer, and the

difficulty in estimating surface area. However, it can enable getting an idea about gold content by

using following formula: X = (1000/W) x S x T x 19.3

X = Total gold in gram / per Kg scrap

W = Part weight in grams

T = Thickness of plated material in cm (XRF test)

S = Estimated surface area of the part in cm²

Ƥ = Gold density 19.3 g/cm² (constant)

Example #1:

We have a ball with a diameter of 0.5 cm, weight of 0.6 g and thickness of 2 µm.

We calculate:

S = π D² = 3.14 x 0.5² = 0.785 cm²

T = 2 µm = 0.0002 cm

W = 0.6 g

X = Total gold in gram per 1 Kg Scrap = (1000/0.6) x 0.785 x 0.0002 x 19.3 = 5.05 gr/Kg

Gold plated thickness can be analyzed with XRF (some XRF does not have this application).

For your convenience, please use our Gold plated parts Calculator   

* Note: 1 µm = 0.0001 cm

Example: # 2  (according to the below picture)

In order to estimate those “windows parts” made of brass, gold plated (with Nickel coating layer preliminary to the gold, as a block layer, so the gold will not diffuse into the brass over the time).

 First we have to identify parts weight & gold layer thickness.

Three important parameters

Calculating the surface area –    (in this case, it is relatively easy as the parts are symmetric and easy to measure) according to our calculation, the surface area is 3.6 square centimeter.

The weight of each piece –   we weighed 10 pieces, then divided to 10, in order to get an average (as not all parts have the same weight) – we have received, 1 Pcs. weight is 1.87 gram.

 

Thickness of the plated layer – we use the “Fischerscope X-Ray XDL 23” (or similar device) – we took 12 different measurements, of few parts (at different spots on the parts) an average thickness measurement was 0.528-micron meter.

1 micrometer is equal 0.0001cm so, measurement result is 0.0000528 Centimeter.

Now let’s calculate how much gold we have in 1Kg of those

“Gold plated items” –

Total surface area per 1 kg parts =   3.6 X  1,000/1.87=1,925 square cm.

(1,000 / 1.87 is the number of parts in 1 Kg.)

The formula for calculating the gold content in 1Kg parts:

 (surface area) x (coating thickness) x (gold density) = Gold (gr/Kg)

1,925   x      0.0000528    x     19.3        = 1.96 gr/Kg

Density of gold is 19.3 cubic cm.

We can estimate that these parts contain 1.96 gram of gold  per 1 Kg. of plated parts.

The photo below shows the same results, when using our calculator.

A.G. Metals is a leader in the field of precious metals, with over two and a half decades of experience specializing in the trading & recycling of precious metals.

 

Ami Gur

A.G. Metals Ltd.

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