JewelLoop · Bench tools

Alloying calculator

How much fine metal and alloy to put in the crucible: to make a new karat, to raise or lower one you already have, or to bring mixed scrap to a standard. For gold, silver, platinum and palladium, with the result checked against the legal tolerance.

Metal and target

Target standard Fine metal you use

Quantity

Finished weight (g)

Alloy to add

Margin and melting loss

Aim above the standard by (‰)Aiming a little over gives room for error; the UK allows nothing under the mark. Melting loss (%)Your own workshop's figure; it varies with method and metal.

Red: under the mark (no tolerance in the UK). Amber: the 3 ‰ US allowance for gold. Green: at or over the standard.

Reference

How far under the mark is allowed
Where	Rule
United Kingdom	No negative tolerance: an article must be at least the fineness it is marked with, or it cannot be hallmarked (Assay Office).
United States, gold	Since October 1981: not more than 3 parts per thousand under the mark, or 7 with solder assayed in (15 U.S.C. §295).
United States, before 1981	Half a karat under (one karat with solder) was allowed: older scrap marked 14K can assay well below 585.
Elsewhere	Check the national rule; see the hallmark decoder for marks and standards by country.

How it is worked out

Make a new alloy

Fine metal = finished weight × target ÷ purity of your fine metal. The rest is alloy.
18K, 100 g, 999.9 gold: 100 × 750 ÷ 999.9 = 75.01 g gold + 24.99 g alloy

Lower the karat

Add alloy (containing none of the metal you are refining) = weight × (present − target) ÷ target.
50 g of 750 → 585: 50 × 165 ÷ 585 = 14.10 g alloy

Raise the karat

Add fine metal = weight × (target − present) ÷ (fine purity − target).
50 g of 585 → 750, 999.9 gold: 50 × 165 ÷ 249.9 = 33.01 g gold

Scrap lots

The mix fineness is the weighted average: Σ(weight × fineness) ÷ total weight. Then it is raised or lowered as above.

Fineness is by weight, in parts per thousand (‰). The crucible drawing shows the charge by weight, not volume. Estimates for guidance; verify before production.

Sources

Gold colour compositions: ISO 8654 / EN 28654 informative table as reproduced by Progold, The colour of gold alloys (AIM 2004): 0N 585 gold / 300–340 silver, 1N 585 / 240–265, 2N 750 / 150–160, 3N 750 / 120–130, 4N 750 / 85–95, 5N 750 / 45–55, copper the remainder. The calculator uses the middle of each silver range. 22K yellow 916.7 gold / 27.6 silver / 52.8 copper: Henderson and Manchanda, White Gold Alloys: Colour Measurement and Grading, Gold Bulletin 38/2 (2005), the measured sample.

Tolerances: 15 U.S.C. §295 (National Gold and Silver Stamping Act, as amended effective 1 October 1981), summarised by Stuller; Assay Office London, Hallmarking guide (no negative tolerance). Standards (375, 585, 750, 916, 800, 925, 958, 850, 900, 950, 500): UK Assay Offices and the JewelLoop hallmark tables. Sterling silver: 925 parts silver, traditionally with copper. Ingot colours: illustrations from the measured CIELab values used on the Gold Colour Lab page.