To purchase Messel fossils with confidence, you must be more familiar with the real thing than the guy who's making them.
As the shale from Messel is fragile, the most frequent method for removal of these fossils is by setting the fossil in a plastic resin. The fossil with part of it toughened is soon extracted from the rest of the rock and taken back to a lab where it is prepared. The preparation is done extremely carefully with dentist tools. It is in this preparation that some people use the wrong tools and destroy the fossil forever when it goes wrong.
There are a number of specific warnings that you must consider when purchasing Messel fossils. There are 3 different types of fossils that occasionally turn up on the open market from the Messel area that should always be avoided. This is because of their lack of authenticity.
Given that the authentic Messel fossils are prepared and preserved in resin, it is extremely simple to construct fakes. These are insignificant casts, with no value, and it is vital that you are able to identify the disparity.
An important tip into knowing whether it is genuine or not, is to look for minute detail on the bones or soft tissue under a microscope. From time to time, the untreated remains hold a variation of colours. Never deal with someone who’s all their Messel fossils are of the same type of animal (e.g. snake) or look to be the same colour. They are most likely not real, but fakes.
The 3 groups that turn up on the open market often are:
1. Messel fossils which are pure plastic resin moulds of the real fossil, so just a resin cast. It is effectively just a copy of the real fossil. Dishonest collectors previously did this a lot when it was made accessible to the public at the pit. So lots of people found these fakes. From time to time, these fake pieces from then still appear on the open market.
2. Messel fossils which have had most if not all of their fossil material destroyed, and so not present by inappropriate lab preparation. This is leaving only the resin cast and not any genuine fossilized animal in the resin block. Where the fossil once was is coloured to make it look as if the fossil is present.
3. Messel fossils which are plastic resin copies made from a silicone mold of an authentic fossil. Silicone will keep hold of the finest detail of the original fossil, and so it is incredibly simple to make an exact copy in resin. The fossil section is then dyed to hide the plastic resin. These are the hardest to distinguish the real from fake.