When calculating the value of your scrap gold, you will first have to figure out just how much gold you really have. The large majority of jewelry that looks like gold is really gold-plated or even a look-alike. If you expect to simply weigh it and multiply it by the current gold price, you will be deeply disappointed.
How to determine the purity of your gold
= Karat =
On many pieces of jewelry an official stamp will indicate the karat purity of your gold. The karat measurement represents the ratio of gold to other metals.
Absolutely pure gold is 24 karat (24K), but this is rare because pure gold is too soft for jewelry and loses its shape easily. Other karat markings could range all the way down to 10K, which means that the piece is 10/24 pure gold. The karat ratio is based on mass, so remember to reduce the total weight proportionately when weighing this piece.
Colored gold is never pure. This is because gold has to be mixed with another metal to get that color. In most cases, colored gold will not be higher than 20K, and will usually be 14K or 18K.
= Millesimal fineness =
On more modern jewelry and virtually all bullion, you might find a different kind of stamp which is somewhere between 333 and 999.999. This measures the purity of gold by parts per thousand.
The first number (333) is equivalent to 8 karats, and is the minimum standard for officially calling a piece gold anywhere in the world. (In the U.S., 10K is the minimum.) The purest gold which has ever been refined is 999.999 pure, but this will never be seen on jewelry.
In some cases, you may see a stamp which combines the karat and the millesimal fineness systems. The karat marking is followed by three numbers which indicate the gold purity percentage. For example, 18K 750 is 18-karat gold with a purity of 75.0 percent.
= Density test =
The density test was originally discovered by Archimedes, when he apocryphally shouted out the word “Eureka!” According to the story, he was also trying to determine the percentage of gold in an item.
To use the density test, you will need to know the exact weight of your piece in grams, and you will also need a small measuring vial with measurements in milliliters. Partially fill the vial with water, then place your piece into the water so that it is totally submerged, and measure how much water is displaced. Then divide the mass of your piece by the volume of displaced water to get your density. The accuracy of your results will depend on your precision in measuring.
The density of pure gold is 19.3 grams per milliliter. If the piece does contain gold, then the higher the density, the purer the gold. White gold has a wider range of densities than the same karat value of yellow gold, because of the different alloys.
This test is not perfect. It only works for pieces which do not have any gemstones. Some large pieces of gold jewelry are hollow, which will invalidate the test. There are also a few non-gold metals used in jewelry which are very dense. In some cases, these metals have been used specifically to fool the density test.
= Other tests =
If you don’t have an official stamp to go by and the piece of jewelry is large enough, you might be best off to have its gold content formally evaluated by a jeweler. Otherwise, you can try to determine whether a piece is gold or gold-plated at home with a few simple tests.
First, examine your items visually. If you see any discoloring, that item is either gold-plated or something else that only looks like gold. Discoloring shows up first on the edges and in other places that are constantly rubbed.
The streak test may scratch your item. However, if your item leaves a black streak on an unglazed ceramic tile, it is not gold.
Gold is not magnetic, so if your piece attracts a magnet, it isn’t real gold. A refrigerator magnet is too weak for this test, so you will need something stronger to see if there is any reaction. However, even if the piece is not magnetic, that still doesn’t prove that it is gold. Other metals are non-magnetic as well.
The acid test is very reliable, but do not use it unless you know what you are doing. The test is that nitritic acid is highly corrosive, but leaves no mark at all on solid gold. However, if your jewelry is not real gold, you could damage it permanently. Depending on the purity of gold or type of base metal, you could get a brown, green, or milk-colored reaction. Never use more than a single drop of nitric acid when attempting this test.
Calculating the value of your gold
After you know which pieces contain gold and how pure that gold is, divide them into piles according to their purity. Measure the weight of each pile in grams, and adjust the weight for the purity of the gold in that pile by using the karat or millesimal fineness ratio. If you need to convert grams to ounces, one troy ounce equals 31.1 grams.
Now that you have an approximate weight in gold, you can multiply it by the current gold price. This will give you a base figure for the value of your scrap gold.
However, you will not get this amount from any scrap gold dealer. They will take their cut as well. A reputable refiner will give you between 90 and 98 percent of the base market value, although they may have weight minimums. Commercial scrap gold dealers and pawnshops will give you between 30 and 60 percent.
Do not forget to remove any gemstones before committing to a deal. Gold coins and antique jewelry may have a higher value than its gold scrap metal.