How to Choose an Air Pen


 Which air pen is right for me? How to choose a fossil preparation tool. How to choose an air pen. Fossil prep air scribe. 

There are an awful lot of names floating around describing the same tools, or the same name describing different tools! You have probably come across the terms air scribe, air pen, pneumatic chisel, pneumatic hammer, air engraver or air incisor. Essentially these all describe the same type of tool - a compressed air driven stylus or needle that repeatedly hits the rock many thousands of times per minute, removing matrix from your fossil. In our neck of the woods, we tend to call them air pens; but you can call them whatever you want!

Each pen consists of a body (the bit that sits in your hand), the head socket (the bit you hold like a pen), which holds a bushing, which in turn holds a stylus (the needle or the nib).

Different tools do different jobs, and have different internal mechanisms which make them exceptionally good at some jobs, but relatively poor at others. All of our own-brand tools at ZOIC PalaeoTech are custom designed to fulfil a need in fossil preparation, but we do our best to make them as versatile as possible to maximise their usefulness. Whilst there are ‘general purpose’ tools to suit somebody just getting started, many professionals or advanced vocational fossil preparators have a myriad of tools; each with its own very specific niche in their work.

Quick links:

Powerful or gentle? The two types of Internal Mechanism.

What to look out for when choosing a new or second hand air pen




The two types of air pen - which one suits your needs?

All air pens in fossil preparation are variations of two different internal mechanisms. Whilst it may seem a little information overload, a very basic understanding of these internal mechanisms will arm you with the knowledge you need to make an informed choice.

There is no set terminology that we have found which differentiates one tool from another; but they categorise into two general types. Whilst you may not need to understand how each type works, it makes a big difference depending on what you will be preparing and your successes with such.


We call these types Impact Driven and Pusher Plate Driven.



1. Impact Driven Fossil Preparation Air Pens (internal piston)

These are the powerhouses of the fossil preparation world. They remove matrix effectively and work well on hard rocks.

How do they work? These function by the inflow of compressed air causing the repeated striking of a piston against the internal end of the stylus, controlled by balancing pressures in internal air galleries within the tool. It is a bit like striking an anvil with a hammer, many thousands of times per minute.

Below, see a diagramatic explanation of how an impact-driven air scribe works.


With some of these impact-driven tools, like our ZPT-TR and ZPT-CP, as a result of the internal mechanisms they are much more powerful than their pusher plate counterparts and some are also able to work at much lower air pressures (low PSI) with considerably less air consumption. In fact, the low pressure tools (such as the ZPT-TR T-Rex) are significantly more powerful than their high pressure counterparts. 

When carefully engineered and manufactured, impact driven air pens have the lowest air consumption of any fossil preparation tool on the market. We're proud to have the lowest air consumption tools on the fossil preparation market. 

There are two main types of air pen within this category. Some have their optimum working pressure set much higher, and others work at very low pressures. This is a result of the size of the piston. At low input pressures, the pressure exerted on the surface area of the ZPT T-Rex is much greater than that exerted on that of the ZOIC Chicago (a modified Chicago Pneumatic CP-9361), because the surface area of the piston is significantly larger.

  • Low pressure tools (such as our ZPT-T Rex), funnily enough work at very low air pressures. They are therefore able to work with much smaller compressors. They are quiet and economical to run; and require your air compressor to ‘kick in’ much less often. These tools have an optimum pressure range of 0.5-3.5Bar or 7-50PSI, and are significantly more powerful at matrix removal.

  • Models like the Chicago Pneumatic CP-9361 (check out our version modified specifically for fossil preparation - The ZOIC Chicago; other variants include the Ken Mannion TT and the Paleotools ME-9100) are impact-driven and work at high pressures, but depending on the modifications performed, should retain low air consumption (our ZOIC Chicago runs on just 6 litres of air per minute!). These have an optimum operating pressure of 6.2 Bar or 90 PSI. 

These tools are well suited to harder matrix as well as allowing more flexibility in their design where one tool body can be adapted to use varying stylus diameters. The downside of these tools is that they are less compatible with more fragile fossils and softer matrix as the force exerted is that much greater. They are a better choice if noise is an issue, as the air compressor will ‘kick in’ much less frequently and at lower pressures, the noise of the tool is at a much lower pitch. Pusher plate tools are associated with a much higher pitched noise, which is somewhat screechy (the CP-9361 can have the same issues - which is why we fitted the ZOIC Chicago with a silencer).

  • Powerful matrix removal
  • Less noisy at lower pressures
  • Good with hard matrix
  • Better with less fragile fossils
  • Lower air consumption
  • Much cheaper to run



2. Pusher Plate Driven Air Pens 

These are best used for more delicate fossils and more detailed work, especially with softer matrix. Ideally, you will not remove large amounts of matrix with this type of tool, but would typically use it on a harder rock once you have used an impact driven tool to get close to a delicate fossil (e.g. a spiny ammonite in a hard limestone nodule). In the ZOIC PalaeoTech range, we call the pusher plate driven tools the ‘raptor’ series - the Velociraptor and the Microraptor are small but sharp and vicious when needs be!

 How do they work? Compressed air enters the body of tool and builds up pressure against the pusher plate which is attached to the internal end of the stylus, and is sealed by rubber o-rings. When the pressure overcomes the spring force of the spring the stylus is pushed forward. The pressure is then released and vented through the exhausts, and the spring returns the pusher plate and stylus and o-rings back into their starting position many tens of thousands of times per minute.

Check out the diagrams below:


This is a gentler action that the impact driven tools, as air is being used to push the stylus rather than the repeated tapping of metal on metal. They therefore remove less matrix at a time, and models with higher beats per minute (bpm) can act to pulverise the rock in their path rather than chipping the rock away giving you more control. They vibrate less enabling you to work with more delicate fossils, and the body of the tool is typically lighter. 

Our pusher plate models include the all-rounder ZPT-VR The Velociraptor, and the ultra-precise ZPT-MR The Microraptor

These tools usually have a high air consumption than the impact driven counterparts. Therefore you would need larger capacity air compressor. They should not be used for extended periods with a 24l compressor. The internal o-rings do wear out (they’re seriously put to work!) and so they will need changing when worn. These tools are slightly higher maintenance in this respect than impact-driven tools but none of this maintenance is difficult or time consuming - we’re always here to help.

  • Perfect for detail and finishing work
  • Less vibration and more control on delicate fossils
  • Work best on softer rocks
  • Cheaper than impact-driven counterparts
  • Noisier



Second hand air pen scribe for sale secondhand

When choosing, there are a few physical things to look out for in both new and second hand fossil preparation air pens or air scribes. A quality tool will last you many years (even decades) when looked after. These following bits of advice apply when choosing a new or a second hand tool – naturally a second hand tool will show wear and tear more obviously than a new one, but there are a few indications of how a tool might hold up over the years.


The first major thing to think about is how appropriate the tool you're looking at is for fossil preparation. Bear in mind that not all air scribes are suitable for fossil preparation. Fossil preparation tools are typically designed specifically for that purpose, or modified from mass-produced metal engravers. An unmodified version (like the CP 9361) works reasonably for fossil preparation and many people choose to use one with enormous success, but a longer, more slender stylus and more supportive bushing are recommended for working with rocks. The ergonomics, silencers, extended reach of nib and enhanced resistance to wear and tear make a modified version a better option.

chicago-pneumatic.jpgIf you see a metal engraver or air scribe, don’t just assume that it will do the job just fine, particularly if the nib is rather blunted with only a tungsten carbide insert rather than full tungsten carbide – you won’t be able to sharpen it into a useful point or chisel. Avoid altogether if the nib is made of steel – it doesn’t stand up to the abrasion. 


The stylus should not wobble in the bushing – when this happens, more kinetic energy (power) is lost from side to side and not fully directed forwards. It is also harder to use a wobbly stylus as you can never be too sure where it is going to end up, on the rock or on the precious fossil!

If the bushing hasn't been sufficiently hardened during the manufacturing process, the stylus will develop a bit of personality. Our tools are all made to have a precision fit between stylus and bushing, so that maximum power is transmitted forwards and allows for maximum control. We harden and temper the metal (you can see that the bushings in the ZOIC Chicago, Microraptor and Velociraptor are either a bluey or yellow colour – a side effect of this process - the T-Rex bushing is internal!), so that it will last you donkey’s years even with the heaviest use.



Another factor to pay attention to is air consumption. Not only does a lower air consumption mean that the tool is cheaper to run (running off a cheaper compressor, and allowing for the compressor to kick in less) but can also be an indication of manufacturing quality.  Air consumption is dictated by the style of internal mechanism to a certain extent, but within a line up of comparable tools, the lowest air consumption for the internal mechanism means that there is less space within for air to be ‘wasted’ and escape. The tighter the engineering tolerances, the lower the air consumption. We pride ourselves in quality of workmanship and our tools have the lowest average air consumption of any range on the market. 





ZPT-MR The Microraptor



Pusher Plate

ZPT-VR The Velociraptor



Pusher Plate

ZPT-CP The ZOIC Chicago



High Pressure Impact-Driven

ZPT-TR The T-Rex



Low Pressure Impact-Driven



The devil is in the detail. Have a closer look at the knurl, wherever present. A properly made knurl has sharp tips and good definition. You’re looking at very small diamonds, meaning that the knurl was cut to full depth, rather than a scored diamond shape pattern with flat tops which doesn’t provide much in the way of enhanced grip. A properly made knurl is extremely easy to hold, meaning less fatigue when working. A minor detail, but another excellent indicator of quality. 





We very much hope that this guide has been helpful. It's important to understand some of the technicalities of how these tools work, in order to get them to work their best for you. We find that the best results are acheived by using a range of air pens, but obviously this is not appropriate for all budgets. The ZPT-CP ZOIC Chicago and the ZPT-VR Velociraptor are great standalone tools; the Chicago for harder rocks and the Velociraptor for softer rocks and more fragile fossils. The T-Rex is a great all-rounder and very versatile with its range of nibs, but is best for more sturdy fossils in harder rocks. The Microraptor is perfect for really fine and delicate work. Many of our customers find that their most frequently used combination are their T-Rex and Microraptor which will suit most jobs!