Collectors are often challenged with cleaning up new invertebrate fossil finds. Two common tools are air scribes and micro abrasive cleaning systems. Air scribes are small compressed air driven tools for removing bulk matrix and general cleanup. Every attempt should be taken to avoid touching the fossil specimen directly, during this stage of cleaning; as this has the potential of damaging your fossil specimen. A micro abrasive cleaning system is used to remove the remaining matrix material. There is an art to this technique. Most collectors practice micro abrasive cleaning on damaged fossils to learn the best techniques. This includes experimenting with abrasive media, such as aluminum oxide grit, dolomite powder, plastic spheres, or baking soda. On this page, I will be presenting updates to collectors on recommended techniques for cleaning invertebrate fossils.
Second Topic : Abrasive grit ( blasting abrasives )
Where to obtain ?:
The majority of the fossil cleaning for Woodbine ammonites, is using a 240 grit Aluminum Oxide product. Large bags are available from International Surface Preparation. My local source is located in Dallas Texas.
How to use/re-use:
I load my abrasive unit with the 240 grit aluminum oxide using a small plastic funnel, with a small plastic scoop. Depending upon your setup, you can use up the initial batch of grit in about 1 hours time. When ready, I will scoop up the grit in the abrasive cabinet and sieve the grit thru a Size 80, Dia 5, US Standard Sieve. This removes large debris, dirt and other undesirable particles. You will notice that re-using the grit extends its life and the grit becomes less abrasive with time. This can be good, as some fossils require less matrix erosion to bring out the features.
Grit used for echinoid cleaning:
Dan Woehr with Paleo Purveyors of Texas will use baking soda 90% of the time. Its a soft media, when compared to the Mohs hardness scale, and does a good job cleaning up Cretaceous and Pennsylvanian echinoids veneered in soft matrix. Cost for baking soda is very much less than aluminum oxide. Dan will recover the baking soda using a cheap frying pan splatter screen. The coarse work in cleaning fossils can be enhanced by using a 0.060 orfice. Its more forgiving using recycled abrasive products. For fine work, using an orfice of 0.030 will require virgin baking soda or aluminum oxide grit. Often, you will find that aluminum oxide grit will eventually burn thru your tungsten carbide tip. This is less of a problem using baking soda.
Where to dispose of old abrasive grit ?:
Most grit can be tossed into the garbage bin, or tossed into the yard. Don't do this with baking soda, as it will kill your well groomed yard.
First Topic : Cleaning Echinoids by Dan Woehr (Paleo Purveyors of Texas) ( December Fossil Factory News )
Method A: Brass brush & water
- Cheap, easy & mobile, this method works well on soft matrix. Brass is soft enough that it doesn't scratch the echinoid test. Don't substitute a stainless steel brush or you will end up with unsightly scratches and obliterate minute detail.
Method B: Air scribe
- Two air scribes are used : Chicago Pneumatic knockoff by Paleotools called ME-9100, and a ARO scribe. The ME-9100 is the workhorse which does most of the gross work. The ARO is used for the fine detail work. Cost ranges from $250 to $300 (USD) with all accessory parts. Each unit is equipped with a long stylus to allow work nearly parallel to the surface of the specimen, without pecking holes in the surface. In general, the air scribe removes most of the matrix, leaving just a veneer which is then removed by one of the other methods described. The air scribe technique can be used in open air rather than in a blast cabinet, but keep area well ventilated ( to keep dust outside ) and wear a dust mask.
Method C: Microblaster
- Low end micro abrasive units such as Eco Blaster from Crystal Mark or Micro-Jet 200 from Hunter Products Inc. are available. Approximate cost is $ 450.00 (USD) for air hose, media canister, foot pedal, pencil tip handle which accepts screw-on orifices. No independent control of of media flow is used, so the user must set the compressor at 125 PSI and blast away. For echinoids, a orifice size of 0.060 inch is used 90% of the time. Finer detail and the tip is changed to 0.030 inch for cleaning between spines. The tips or nozzles are made of tungsten-carbide. 90% of the time, baking soda is used as the media. For more tenacious matrix, dolomite media is used. Much of the work is performed in a low-end blast cabinet from Harbor Freight. The cabinet has a port for the micro-abrasive hose, a clear window, removable top, ventilation port, a bright light, and front hand access holes. A shop vac can be used as the dust collector. Other home-made setups are possible depending on how far you would like to move the exhaust. The media is recovered, sifted and reused by using a set of brass sieves, or a cheap frying pan splatter screen. The air compressor usually has a air-dryer installed in-line to remove moisture. With out this feature and the daily task of emptying the water out of the air compressor, your air abrasive media will clump and not work.
Method D: Potassium hydroxide (KOH).
- This stuff is caustic so wear goggles and gloves, and use it in a well ventilated area. KOH is available in flake form from chemical supply houses in 5-pound plastic bottles to 50 pound bags. Keep the stuff sealed as it is hygroscopic ( readily absorbs moisture). Place echinoids in an old Pyrex dish, spray them with atomized water to help the flakes stick, dump the flakes on them to cover all the unwanted matrix, spray them again, and check them every 20-30 minutes, flipping them as required. KOH creates an exothermic ( heat-releasing ) reaction with water that turns certain forms of calcareous matrix to sludge. It is possible to overcook your echinoids, creating micro-cracks and a bleached surface with reduced detail, so watch the time. I tend to wash them off after a while, air-scribe a little more matrix and repeat the KOH application as required. A gelatinous, caustic slime will cover the specimens so scrub them under the hose with an old plastic brush while wearing gloves, and then drop them in vinegar for 10-15 minutes to neutralize the KOH, and after another water rinse, they are finished. Keep in mind that in some formations, KOH attacks the test.
In the above photo, you will see a Micro-Jet 200 air abrasive unit. The canister holds the abrasive media, which must be changed out if you switch from one type to another type.
In the photo above, you will find two types of air abrasive cabinets that are commercially available. Many collectors will fabricate a blast cabinet out of plywood and implement special features for their particular workspace.