We can see many deals being offered at different auctions sites, offering us anywhere from scrap Gold Filled (GF) watch cases/bands to pins and other decorative ornaments. In many cases a confusing or plain wrong weight measurements are used to describe the items in order to get the buyer to base his calculations on inflated numbers. This article was written to prevent that.
We should probably get familiar first with the known Gold Filled standards and how it's made:Basically and without going through the entire production process, Gold Filled is a thin sheet of karat gold (10K, 12K and 14K) which is fused to a thicker sheet made out of base metals of different alloys such as Brass/Bronze. Sterling Silver is also used, though less common.The process usually involves rolling the two sheets together to a desired thickness (hence the synonym: Rolled gold).Together, these sheets are formed into fairly rigid, hollow shapes and enjoy a protective cover (and looks) of a noble alloy but at a fraction of the price of an actual Gold jewelry.
1/20 12K - What is that??
The first numbers (1/20) indicate the ratio between the mass of the Karat Gold sheet to the mass of the entirepiece (karat + base metal) at any given dimensions of the Gold filled sheet.Clarification: Surface area does not play a part for calculating Gold Filled value. Whatever size or shape you cut the Gold Filled sheet, the ratio by mass remains the same.The second number indicates the karatage of the Gold sheet alloy.Now, say we want to know how much actual gold is there in a sheet of Gold Filled.Example:How much gold would there be in a 100g stamped sheet of "1/20 12K" Gold filled?
1/20 = 0.05 (or 5%) 100g x 0.05 = 5g12K = 12/24 = 0.5 (or 50%)5g x 0.5 = 2.5gThe answer will be: 2.5g of pure gold.These are the exact steps our Gold Filled Calculator uses.
But wait, keep reading…Mainly, there are three agreed mass ratios of which a sheet of gold would be considered as Gold Filled. Minimal karat should be of 10K.1/5 - 10K , 12K , 14K1/10 - 10K , 12K , 14K1/20 - 10K , 12K , 14KThough 9K pieces are not officially recognized as Gold Filled, it is very common to find that kind of jewelry circulating around and stamped as GF scrap.Any figure above 1/20 (at any karat) will not be considered as Gold filled as well, it is now called Rolled Gold Plate (R.G.P) or Heavy Gold Plate (HGE) and usually is marked that way.The known gold to base metals ratios for R.G.P are: 1/40 and 1/50Karat ranges from 10K to 18KNote: 18K Gold Filled is not common in many countries. Had it been offered to you, it will be wise of you to suspect it to be R.G.P rather then Gold Filled. The calculation remains the same though.
From theory to practice.