Real vs. Fake Amber
Fake amber is not hard to make. It can be made from heating colored plastic, using copal (not 'mature' amber) or other modern polymers. Amber that looks 'too perfect' probably is! Quality specimens run into the thousands of dollars.
It is not particularly easy to identify fake amber from real amber. So, how does one determine if you have a real sample of amber?
First, one must understand that amber is the fossilized resin from ancient trees. In the Dominican Republic, the tree is Hyemnaea (a leguminous trees). Most modern legumes are smaller plants that have nodules in the roots which contain bacteria that put nitrogen back into the soil; peas, and clover are legumes. Modern day legume trees are common in South America. In the Baltic area, millions of years ago, either pine trees or eucalyptus (gum) trees probably produced the resin that turned into amber.
Resin from either of these types of trees, when placed in the proper conditions, turns into amber. There is an intermediate stage where the resin might look like amber, but is not changed enough (polymerized) to be considered real amber. This 'young' resin is called copal. Copal is always much younger than amber and has some characteristics which distinguish it from real amber. For instance, copal is generally less dense than amber.
Density is measured in something called specific gravity. Regular amber often has a specific gravity of 1.05 to 1.10 (where 1 is the same as water). Copal looks similar, but has a lower specific gravity of 1.03 to 1.08. A specific gravity of above 1.0 will cause the object to sink in fresh water. While amber and copal will both sink in regular water, salt water has a higher density. Amber and copal will both float in salt water. Roughly 15 grams of salt in 100 mL of water (4 teaspoons of salt to 8 ounces of water) will approximate salt water. In this solution, both amber and copal should float. Copal is usually lighter than an equal volume of amber. Unless you are very familiar with the weight of amber, don't trust your estimate of the weight.
One fairly good way to determine fake amber is the 'hot point test'. This is where the fine point of a very hot needle is put in the amber. Real amber has a piney smell (or burnt resinous smell) and fake amber can have an electrical, plastic or sweet smell to it. The problem that you will have with this test is that most folks are not willing to sacrifice their potential prize piece of amber to this test.
Equally as bad is the burning test: amber burns with a black smoke, copal will burn with a whitish smoke, plastic immations can also burn with a black smoke. Again, who is willing to sacrifice their sample to this rather harsh test?
Another test is the acetone test. Acetone is the odoriferous chemical that is used to remove nail polish. Copal is slightly soluble (hasn't hardened enough over the millions of years) in acetone, so the surface will get sticky. Regular amber is not soluble and therefore acetone should not do anything to it. With plastic fakes, acetone can dissolve the outer layer, which can sometimes be a shellac coating. This is probably one of the easier tests.
Difficulty does arise when the creator of fake amber will drill out the center of the amber piece, insert a modern insect and then fill the hole with hot copal. The resulting piece is very hard to distinguish from the real thing. If the light is perfect, one may see the original drilled hole, but don't count on it. Identification of an extinct species of insect is difficult unless you are an expert entomologist! 'Old' and 'new' insects all look the same to the untrained eye.
For the geologists, amber has a refractive index of 1.5 to 1.6 (copal also is the same) while fakes of plastic and other chemicals will give a very different refractive index. The refractive index is a measure of how light is refracted when it goes through the amber. In order to do this test, you need a refractometer (a gemological instrument).
Amber is fluorescent. That is, when ultraviolet light (UV) is directed on the amber, it will fluoresce. Common fluorescent colors are yellow, blue, green and orange. The intensity of the fluorescence can be different with different types of amber. Dominican Republic amber usually fluoresces blue. This is a simple test if you happen to have a black light. Just shine the black light on the sample and observe the 'shine'.
Amber is not hard, when using the Moh's scale. It ranks usually from 2 to 2.5. Your fingernail is about 2 and thus it is very difficult to scratch amber. An American penny has a hardness of 3.0 and should scratch amber. Steel wool, which has a hardness of 5.5, when scraped on amber produces powder or very fine granules. If the piece is plastic, shavings will likely result.
Raw amber, when broken has conchoidal fracture. That mean is looks similar to chipped glass. A chipped piece of glass will often show concentric circles in the chipped area. That is conchodial fracture. Amber does not have to chip in this fashion, but often will exhibit the type fracture cut.
Lastly, there are some pieces of amber in gem stores with 'spangles' in it. This is attractive amber that has small disk shaped 'inclusions'. The spangles are not natural. A few years ago I saw some Baltic amber in a jewelry store. When I asked about the iridescent , sand dollar shaped inclusions, I was told that this was a natural occurrence in the amber. Wrong. This is made by heating amber in rapeseed oil. The sun-spangles are thought to be from droplets of water which were trapped in the amber. The droplets flatten and assume the spangle shape. Some of the samples that I have seen are quite attractive! So, if you are after a beautiful piece of amber, the spangles are great, but don't be fooled into believing that they are a result of a natural occurrence.
Your best bet is to purchase amber from a reputable source.