Fossil Prep - Paraloid B-72
I get asked a lot (especially through Instagram and Youtube) about the equipment I use to prepare fossils and to protect them during the process of removing the matrix. I'll add a blog soon on the equipment I use to remove the matrix (like the air abraders and air scribes), but the most important equipment in my armory is the liquid I use for consolidation, finishing and adhesion - Paraloid B-72 (formerly known as Acryloid B-72).
As you work to expose the fossil material which has laid untouched for millions of years, it's only natural that there will be fractures, fissures and broken sections. As you remove more matrix, the vibrations of the pneumatic airscribes will also loosen material so it's important you stablise the fossil material as you go. There are lots of resins and polymers that are used by fossil preparators, but the one I prefer is Paraloid B-72. I prefer this for the following two reasons:
It has multiple uses - It can be used as an Adhesive (to stick fragments back together), a Finishing Varnish (to give a glossy finish is preferred) and as a Consolidant (to dissolve into the fossil structure giving it more stability).
It dries clear, remains clear over time and can be removed very easily with acetone if you wanted to make an adjustment to the finish.
What is Paraloid B-72?
Paraloid B-72 is a durable, non-yellowing, stable clear acrylic resin which is generally purchased as small resin pellets or beads. For the chemistry geeks out there this is an ethyl methacrylate co-polymer. You can purchase this online in large buckets (see links below). Buying dry resin beads (rather than premixed solutions) is important as it allows you to mix solutions of differing ratios/dilutions for differing purposes - such as adhesion or consolidations. This gives you the greatest flexibility.
Getting the right ratios?
Turning these beads into an easy-to-apply liquid is also easy and just requires the mixing with acetone however the dilution ratio is critical. Before any mixing starts, it's important you consider the purpose of your mixture. Are you looking to join two fragments together (Adhesion)? or are you just looking to bring stability (consolidation)? The following table is my rule-of-thumb when it comes to ratios and dilutions:
Purpose: Joining two fragments together just like superglue
Dilution Ratio: 1:1
Example: 50g of Paraloid Bead: 50ml of Acetone = 100ml of Paraloid Adhesive
High Gloss Finish
Purpose: To cover the finished fossil with a high-gloss protective varnish which can also increase the color and contrast of the final fossil.
Dilution Ration: 1:5 (17-20% dilution)
Example: 35g/40g of Paraloid Bead: 165ml of Acetone = 200ml of High-Gloss Varnish
Low Gloss Finish
Purpose: To cover the finished fossil with a low-gloss protective varnish which preserves a more natural look to the finished fossil
Dilution Ration: 1:10 (8-10% dilution)
Example: 18-20g of Paraloid Bead: 180ml of Acetone = 200ml of Low-Gloss Varnish
Purpose: For general use during preparation to give the fossil stability and to stop small fractures increasing in size or small fragments getting dislodged
Dilution Ration: 1:20 (3-5% dilution)
Example: 6-10g of Paraloid Bead: 190ml of Acetone = 200ml of Consolidant
How do you make the liquid?
Once you've chosen the right dilutions for your purposes, the process of creation is pretty straight forward. All you need is the following items:
Paraloid B-72 resin beads
Glass measuring jug (no plastic!!)
Glass Jars (with metal lids)
Measure out the right about of Acetone for the solution you'd like to make (see guidance above). In this example, I'm producing a low-gloss varnish (10% dilution) to give my fossils a protective finish. For this I'll need 20g of Paraloid and 180ml of Acetone.
Pour the Acetone into a glass jam jar (everything must be glass or metal as acetone dissolves all plastics) and close the lid. Acetone evaporates very quickly so it's important to keep the lid closed (oh and it also stinks!).
Weigh out the exact amount of Paraloid B-72 resin beads required for the task. In this case I'm going to need 20g of Paraloid to add to my 180ml of Acetone to give me the 10% dilution I require.
Take a reasonably long piece of cheesecloth (must be cotton cheesecloth and not any plastic mesh) and lay it flat. Then place your Paraloid B-72 beads in the centre and bring the corners together to make a neat bundle.
Open the jaw with the acetone and suspend the Paraloid beads in the cheesecloth mesh into the acetone. It's important that all of the beads are submerged in the acetone to help with swift dissolving. I've found this to be the fastest and most effective way of getting the beads to dissolve. Resist the temptation of just throwing the beads in to the bottom as you'll end up with a undissolved mess at the bottom of the jaw.
After an hour or two, all of the Paraloid will have been dissolved. During this time however, it worth giving the mixture a few stirs to speed up the process. For stronger 1:1 ratios, dissolving time might be longer. Once all of the Paraloid has dissolved, remove the cheesecloth, re-seal the mixture and give it a final stir. Finally, mark up your jaw - it's easy to forget!
This is now ready for using!!
A practical guide to Paraloid B-72:
An online US supplier: