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Preparation

When trilobites see the light of day

Onnia sp. Whenever a layman looks at a nicely done preparation he usually can't help but wonder how it was possible to extract a trilobite from the surrounding rock without inflicting any major damage on the fossil itself. For it is not any sort of dried-up cheese that our beloved bugs are stuck in but usually solid and dense sedimentary rock of varying strength. To make things worse, the most common practice to find trilobites is to chop them into pieces to begin with by cracking chunks of rock known to be fossiliferous.


With some luck, you split the fossil cleanly lengthwise or merely break off the head or tail shield and all you need to do is put both pieces back together, now that you know what's inside. It may also occur that your chunk cracks right at the carapace, leaving disintegrated parts of it stuck in both positive and negative while sending some others onto a flight path to Neverland. In the worst case you simply smash the darn thing to rubble and have to say bye-bye to what used to be a fantastic specimen before you applied excessive force to it.

1.Ampyx 12.Ampyx 23.Ampyx 3
Left to right: 1. Exposing the first of several trilobites on a multiple plate (Ampyx priscus). 2. Preparation of the second specimen at the far right of the matrix. 3. The finished preparation with grinded surface. (larger images)

No matter how skilfully you command your tools and regardless of how much patience you bring to the job – to be a good preparator, you need more than these virtues, you need comprehensive and profound knowledge of the different trilobite morphologies. The techniques used to extract fossils without destroying or damaging them are manifold. Apart from an entirely manual preparation by means of scalpel, stylus and steel needle, in which the rock is removed from the underlying fossil bit by bit by applying adequate pressure by hand, electrically powered tools like grinders and air-pressured chisels are used to work larger areas with good results within an acceptable period of time. Blasters have become more and more popular as they allow for the extraction of even the most fragile and delicate details of a trilobite's carapace, provided the preparator has found just the perfect abrasive – not too hard, not too soft, just right to do the work without attacking the fossil itself. Masters in their fields manage to produce results unimaginable just decades ago.


1.Xiphogonium12.Xiphogonium 23.Xiphogonium 34.Xiphogonium 4
Left to right: 1. Xiphogonium at an early phase of preparation. 2. Work on the positive reveals missing parts of the carapace. 3. Existing parts have been transferred from the negative to the positive. 4. Removal of matrix from the axis. (larger images)


As already indicated, the selection of the right abrasive is crucial to the success of preparation when using a blaster. It must be aggressive enough to remove the matrix but inferior to the strength of the calcified trilobite shell. Not an easy task, but inevitable to avoid irreversible damage to the surface of the carapace. Especially with those frequently offered Russian asaphids bad examples are abundant for it is hard to find a specimen still showing terrace lines – a feature important enough to be used in taxonomic classification. Such trilobites with surfaces as smooth as an infant's behind may be suitable for the mass market but they are all but worthless to any scientific approach. Blasting, when improperly conducted, may turn up with the same awkward results as a bad manual preparation, when the frequently misguided tip of a needle turns even the most resilient of shells into a lunar landscape. Not to mention the notable costs for a good blaster.

1.Stichel 1 2.Stichel 23.Stichel 3
Left to right: 1. Unsuitable needle as frequently offered for sale at fossil shows. 2. Home-made tool, grip built from car parts, with flat chisel. 3. Another home-made chisel with normal, pointed steel needle. (larger images)

Successful manual preparation using steel needles requires certain preconditions to be met. One is that the rock and carapace have been tested to separate easily. Another requisite is that the trilobite's morphology does not require the preparation of too many free-standing spines or other protrusions. As a matter of fact, needle preparation should only be regarded as fine-tuning since other tools need to be applied first to do the rough jobs that precede the meticulous extraction of finer detail. Needle preparation is done using a stereoscope with adequate illumination. Needless to say that the wrong needle will render all other precautions useless.

Präparations-Werkstatt Illus 1: Cheap and pretty much useless chisel as frequently offered for sale at fossil shows, the grip being simply too thin to apply adequate force to the matrix with proper guidance to the tip. Preparing the trilobite with such a tool is a safe bet on an unsatisfying result.

Illus 2: Comparably short chisel, home-made by Dieter Holland, constructed from parts used in circuit tester for cars, bearing a flat chisel as a head. Force is applied by the palm of the hand while the fingers' only job is to properly guide the tool. Allows for hours of stress-free working. Steel needles of two different sizes and shapes are being used: The regular pointed steel needle (illus. 3) for the fossil itself plus the flat chisel (illus. 2) to work the matrix around the trilobite. Every once in a while it should be tested which is the more appropriate one as the character of the matrix may change. Unfortunately the durability of these needles is limited and they have to be sharpened frequently.


1.Destombesina 12.Destombesina 23.Destombesina 3
Left to right: 1. Destombesina in unprepared condition as found. 2. Working towards the head shield, grinding off large amounts of matrix in the process. 3. The almost finished specimen. (larger images)

Mere collectors with no ambitions in doing preparations on their own do rarely get a chance to get an insight into the preparator workhop and the processes involved. Usually, they only get to see the finished trilobites. We therefore would like to show a few examples of fossils at different stages of preparation plus the final results. It may help to at least get an inkling of the time-consuming efforts which go into a good preparation and put prices back into perspective. It may also serve to convince any disbelievers who doubt that anything with an age of several hundreds of millions of years can look as neat and fresh as some fossils do, that there is no reason to doubt the authenticity of such a preparation in general. They may sometimes look too good to be true, yet be true still – and carry a corresponding price tag! ;-)

Addendum: In view of the ongoing discussions between preparators and collectors about the legitimacy of certain manipulations to a fossil (isn't preparation by defintion a manipulation to begin with?) Udo Resch, a preparator of trilobites and others fossils in his own right, came up with the idea of assigning different seals of quality to any fossil for sale in order to let the degree of authenticity be known to any unwary buyer. Since we were not talking about outright fakes here, I decided to act on his proposal and put it up for discussion on this page. Originally Udo Resch posted to our bulletin board on two occasions suggesting what he believed to be an adequate gradation to reflect the different qualities. Klaus Bartl undertook to fine-tune Udo's idea until we ended up with a sort of traffic light-like colour coding system which might be used as a seal of quality by preparators in the future:


Grade
Description
natural

fossil which has undergone but preserving procedures, like reinforcing an all too thin matrix, with no restorations, additives or sealers, original, natural rock

enhanced

fossil which has seen some sort of surface finishing, e. g. darkening, light colouring or bleaching of an otherwise low-contrast specimen

restored

small-scale restorations like casting missing parts of the exoskeleton from corresponding moulds that originally housed the missing piece or pieces

reassembled

anatomically correct rearticulation of slightly disarticulated specimens, accompanied by documentary proof, pictures included, of the original condition and the steps taken

reconstructed

fossil in which missing parts have been reconstructed at the discretion of the preparator without access to a corresponding mould (the so-called "Ceratarges-problem": it usually misses at least one free cheek). Reconstructed parts may be coloured to fit the authentic parts of the fossil

designed

obscuration of the true state of preservation of a fossil by applying opaque coverings as very often can be found in cheap Moroccan preparations. May also include non-authentic reconstructions of missing parts

composed

composition of a fossil by using the disarticulated parts of at least two different individuals or an artificial arrangement of fossils which originally were not found together (e. g. „trilobite pizzas“)

cast

the name says it all: latex and other types of casts taken from the original fossil are quite frequently used to replace a collector's holotype, etc., which is then given to a museum. A cast is no problem unless it gets traded as being the original and therefore with the intend to cheat and deceive.

Surely, it would be of tremendous benefit not only to the collectors community but to the reputation of the fossil trade itself if fossil traders and preparators alike could be convinced to adhere to a gentleman's agreement to use the above classification when offering their fossils for sale. I appreciate the contributions of Udo Resch and Klaus Bartl to this subpage and the set-up of the classification chart.

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Last Update : 06/30/2010 7:45 PM