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What is an Air-Abrasive?

An air-abrasive tool uses compressed air to fire abrasive powder and is an ideal tool for the preparation of certain fossils.  The air compressor links to a pen, similar to an air-brush, which allows the compressed air to be aimed with precision.  Abrasive powder is delivered to the pen and sprays out with the compressed air. 

Benefits and capabilities

Air-abrasive units are found in every professional fossil workshop.  They offer tremendous advantages over other preparation tools and are the tool of choice for many types of fossil.  Air-abrasives are most suited to soft limestone, such as chalk, where the rock matrix is soft whilst the fossil is relatively resistant.  Chalk is soft because the microscopic grains are only weakly held together, so the abrasive powder easily dislodges them from the fossil and one another.  By choosing the correct abrasive powder and the right air pressure, the rock matrix can be completely removed whilst leaving the finest details of the fossil intact.  Such details are often essential to palaeontologists for identifying fossils, but are easily destroyed by other tools (e.g. penknife).  Examples of the level of detailed preparation which can be achieved with an air abrasive tool are shown below.

Equipment

A complete air-abrasive unit is not a cheap set-up and a wide variety of equipment is available, so the enthusiast should research properly before making a purchase.  The tool itself is comprised of an air compressor which is linked to an air-brush-like pen.  The abrasive powder is contained either within a separate canister linked to the pen, or in small container mounted upon the pen itself.  There are a variety of powders available, of various composition and coarseness which makes them variously 'aggressive'.  

Safety

Many are potentially hazardous to health and abrasive work must be carried out within an enclosed unit, typically a box with a transparent lid, internal lighting and holes for hand access.  An air extraction unit is vital to remove the powder laden air from within the work box.  A gas mask, ear protection, gloves and goggles should sensibly be worn too.  An air-abrasive set up is very noisy and dusty and should be installed in a suitably environment, such as an outdoor workshop.

Technique

Aggressive settings can be used to clear large volumes of matrix, but the air-abrasive is best suited for the fine detail preparation once the bulk of matrix has been removed.  Ideally the matrix should be trimmed such that only a very thin cover of matrix remains but the fossil itself remains unexposed and unmarked.  With soft limestone such as chalk this can be achieved with dental tools and toothbrushes.  Generally the air-abrasive pen should be held at a low angle to the surface being worked upon, unless there are delicate surface features such as spines which are best not undermined.  Whilst in action, the pen should be in constant motion as even the least aggressive powder will etch or polish the surface of a specimen if aimed at a single point for more than a second or two.

Pictures & Videos

The following examples show what can be achieved in very short time with a reasonable air abrasive set up.

 

   

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Safety notice: Fossil hunting can at times pose a risk to personal safety, in particular within environments close to the coast, cliffs or in quarries and when using the tools and equipment illustrated. Discovering Fossils provides a free resource to inform you about this fascinating subject and does not accept any liability for decisions made using this information. We recommend all individuals abide by the 'National Fossil Hunting Code' and independently research the potential dangers before and during the visit.

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