Preparation of a Juvenile Ichthyosaur

Preparation of a Juvenile Ichthyosaur

Finally, the blog section of my website is working again, so a good opportunity to write up some notes on the preparation of a juvenile Ichthyosaur sp. that I finished recently.

  Preserved in an extremely hard partially nodulised limestone block from Somerset UK, it quickly became apparent that traditional air tools were not going to be able to separate the hard rock from the fossil bone. In this situation, acid preparation was likely the best way to go about exposing the fossil in all its detail.

When preparing a fossil for acid preparation it is important to seal any areas that you don’t want the acid to remove. This can be achieved with Paraloid B72, wax and silicone.

With this specimen, I have used Paraloid and wax. Paraloid is only semi-permanent so it has to be re-applied every time you take the fossil out of the acid. Wax will create a much more permanent barrier and can be used to cover areas that need to be protected for the duration of the acid preparation time.

Below is a time-lapse of some of the acid preparation. Please click on it to play the time-lapse images.

Also here are some static images in a higher resolution

Above: Shows the fossil after a week in acid

Above: Paraloid is continually re-applied to the bone.This image represents about two weeks of acid prep, but the fossil has been removed several times, dried and paraloided and then resubmerged in acid.

Above: Areas of the fossil are starting to become very delicate. To avoid all the rock surrounding the bones being removed, I start to apply wax to completely seal off some areas from the acid.

Above: The body part will soon be almost completely covered in wax apart from the areas that require further acid prep. It is still important to paraloid the exposed fossil first, this will help in removing the wax later.

Above: After over a month of acid prep most of the body of the Ichthyosaur is exposed. Any further preparation would risk the integrity of the fossil. The wax is completely removed by submerging the fossil in hot water, hot enough to melt the wax so it can be removed with a soft bristled paint brush. The paraloid is also diluted down and partially removed so as to not risk destabilising the fossil.

Above and below: One of the great things about acid prep is that it reveals every detail, even some of the extremely delicate preservation such as skin and stomach contents can be revealed. The lighter yellow areas above and below are likely stomach contents, whereas the darker black areas are possible skin.

Below: Other parts of the Ichthyosaur are also prepared with acid to soften the rock, which makes mechanical prep easier.


Above: One of the rear paddles of the Ichthyosaur. What’s particularly interesting, is the little notch in one of the paddle bones just above the radius and ulnar on the right in this image. This is one of the diagnosic features that helps identify the species.

Above: The other rear paddle is not as complete, most likely lost to coastal erosion.

Above and below: One of the front paddles is quite scattered and one disappearing under the body (below)

Below: Ichthyosaur rostrum elements – sadly lost to coastal erosion, but the preservation has the appearance of being opalised

Below: The various parts are connected together and where the edges meet, they are carefully prepared to make the joins as seamless as possible. These seams (edges) are left to last, to avoid damaging them in the earlier stages of preparation.

Below: Rear portion of the Ichthyosaur

Below: The parts are brought together ready for assembling on a strong wooden board. They are glued and surrounded by resin to protect them and keep the specimen stable.

Below: The finished Ichthyosaur, the preparation being left as natural as possible. At the moment I’m unsure of the exact species, but it could be either larkini, somersetensis or possibly conybeari, but very unlikely to be the later.

Additional notes regarding acid preparation

It is important to use a buffer when using acetic acid. Adding bonemeal to the solution helps keep some of the minerals in place, that would otherwise be removed. This is important for the integrity of the bone.

Also, the fossil should be flushed in running water for at least three times the amount of time it was left in acid. This helps remove the build-up of salts which might later affect the stability of the fossil.