We use archival marking to give specimens or fossils unique numbers or letters, linking them to a separate catalogue record. This allows us to store a lot of information on even the smallest fossils. Museums do this for each specimen they accession (acquire), but you can do this for your personal fossil collection as well. Recording information about your private fossil collection makes it more meaningful. There is no obligation to catalogue or mark your fossils if they are privately owned, but it increases its value (in terms of scientific value, monetary, interest and intrigue, or all of these).  

In the old days, labels were often kept with the fossils but these can easily be lost, misplaced or disintegrate. You will have seen ancient labels stored with old Victorian fossils. It’s hard to imagine that they didn’t look like that when they were first produced! They were probably a nice white colour, with neat edges and no creases, and neatly filled out. Time ages labels very poorly, and after enough time has passed, they usually look like that ‘pirate treasure map’ you made in school,  staining it with tea and tearing the edges. 

It is much simpler and considerably less risky than a separate label, to give a specimen a number, which can belinked to other more extensive records or archives (either in writing, on a computerspreadsheet or in a database). So how do we mark fossils with a number? How can we be certain that it won't rub or fall off? How can we remove it if the fossil changes hands? There are a few guidelines generally followed by museums worldwide. In private collections, we tend to follow the same principles as museums for the same reasons – you want long-lasting, secure, durable, reversible and discreet markings on your fossils. You want the markings to be permanent, but easily removed if intended.

The Collections Trust have a series of guidelines for marking/labelling objects. Source: Collections Trust 2009-2020. These guidelines are linked at the bottom of the page for anyone interested. 

The Collections Trust guidelines cover all sorts of objects that may be found in a museum, from paintings, to textiles, to wood, ceramics, taxidermy, etc. We will be focussing (of course) on fossils collections in this article, but the same principles will apply for geological and mineral collections. 

• Location, location, location! You don't want the marking to be the first thing you see when you look at a fossil, but it's also important to be able to find it quickly when you need it.
• If the fossil is within its matrix, mark the matrix not the fossil.
• Consider the scale of the marking. Whilst a tiny marking on a tiny fossil is appropriate, you don't want to spend hours searching for a miniscule marking on a sauropod femur that's bigger than you. The marking needs to be scaled appropriately for the fossil. 
• With palaeontological specimens, we also must be aware of not obscuring any important, diagnostic or interesting features with our archival marking. For example, if an ammonite has a pathology, you wouldn't put the marking directly over this.
• Avoid weak or fragile structures that may be prone to breaking off. If you are nervous of this, or your fossil is in multiple parts, give each one a number and a suffix (e.g. OBJECT-a, OBJECT-b, and so on). 
• Avoid placing a label or marking over a fracture, mineral vein or previously glued surface. 
• Choose a substrate that is not too porous or likely to be rubbed off - if you only have porous surfaces, make sure the fossil is well consolidated with Paraloid B-72 and that the surface has been strengthened with the resin. 
• If you have to label a box rather than the fossil (which maybe the case with very small items like sharks teeth, or a box containing anumber of specimens under the same collection number), label the box not thelid. It’s very easy to misplace lids, or mix them up. 
• Don’t place the number on an underside surface that is incontact with a surface. As you pick things up and look at them, the number maygradually wear away. If you place it somewhere that isn’t going to be subjectto wear or friction it is considerably less prone to wear. Friction won’tnecessarily dislodge a marking in a year, but after 10-50 years of beinghandled, it’s possible. 

Let's start with what we DON'T use. 

Nail polish formulations vary depending on the manufacturer, but they are exclusively designed for short term use and will yellow and crack in UV light over time. The polymers will cross-link and the marking will be lost. 

By using very specific materials you can acheive a secure, reversible, and stable marking that will potentially last many centuries if not longer. We use a familiar acrylic resin that many fossil enthusiasts will have in their workshop anyway, Paraloid B-72. Other parts of your archival marking kit will have to be sourced especially for the job such as Paraloid B-67 in white spirit. We have archival marking kits for sale to get you started. 

Here is a list of items you might find in an archival marking kit, specifically tailored to geological, fossil and mineral collections:

So how do we put this lot together to come up with something that could last for centuries or longer? We call it an archival sandwich. The plate is the fossil/specimen, and the archival information (the filling) is sandwiched between two different layers of resin (the bread). The topcoat and basecoat always remain the same, but there are different ways of filling the sandwich depending on the specimen and your personal preferences. 

Layer 1: BARRIER COAT

Layer one is Paraloid B-72 20% wt/vol in Acetone. This is the layer always in contact with the fossil or the matrix. This layer acts as a barrier between subsequent layers and the specimen. Paraloid B72 is famous for its long term stability - it doesn't yellow or crack in UV light. Acetone is a fast drying solvent, meaning that you can work quickly. Most importantly, Paraloid B-72 is NOT soluble in white spirit.

Layer 2: THE FILLING

This will depend in part on the substrate (fossil or matrix composition), the colour, and to a large degree personal preference in terms of application and aesthetics. In the same way you might select your sandwich fillings in the morning before work, it's time to choose the best filling for your archival sandwich! We'll talk through your different options in the next section.

Layer 3: TOP COAT

The last layer to be applied is the top coat. We use Paraloid B-67 20% wt/vol in White Spirit. B-67 has good aging characteristics, although it can yellow a little over time. We use a solution in white spirit, as this can be applied directly over the top of the Paraloid B-72 barrier layer without disturbing it. The white spirit is also less likely to disturb any inks used than acetone. 

• Any colour rock/fossil
• Suitable for all substrates
• Stands out well against a background
• Easiest option for rough surfaces where it may not otherwise be possible to write legibly

You may think it's simpler just to print out a ream of collection numbers and stick them on. This may indeed be your best option if you have messy handwriting! However, it's really hard to find suitable printer ink or toner that is permanent. It needs to be durable, resistant to abrasion, not smudge, be printed on acid free paper, be lightfast (i.e. not fade - ideally carbon pigmented), insoluble in water, insoulable in white spirit or the topcoat. 

If the ink or toner conforms to ISO 11798:1999 this means that it is considered permanent and durable. Some manufacturers will list on their websites whether their ink or toner meets this standard, others would need to be contacted. 

Use a titanium oxide based pigment. Titanium oxide is lightfast which means it doesn't fade or yellow. It is considered stable. Golden Fluid Acrylics Titanium White has an easy working consistency, and can be applied with a brush.

Paint a neat little rectangle on top of the barrier coat of Paraloid B-72. Wait until it has dried. You can then write on this with a Sigma Micron marker, an Identi-pen, or lightfast ink. 

• Dark colour rock/fossil
• Suitable for smooth substrates

• Light colour rock/fossil
• Suitable for smooth substrates

Collections Trust, 2020. Labelling and Marking Museum Objects booklet. Download from this link.

Davidson et al., 2006. Assembling an Archival Marking Kit for Paleontological Specimens. Read here