Institutions like B-72 as a base and top coat to sandwich the catalog # because it does not damage the specimen, protects the catalog #, and is reversible with acetone (meaning the label can be removed and ideally does not damage the specimen during that removal IF it ever becomes necessary to remove the label).
I have been managing labs and labeling items for years. Here’s what I’ve learned and my opinions. I prefer to write the catalog # rather than use the paper. B-72 can be written on easily with an archival quality ink quill or pen, but it has to be applied properly.
If the B-72 is too thick when applied, your base coat will bubble and become very “gummy” and not dry properly. B-72 thickens with use because the acetone that is dissolved in it evaporates into the air every time you remove the lid. You have to periodically correct for that by re-adding acetone to the B-72 (how much acetone depends on the size of your B-72 container, and how often depends on how much labeling you are doing with that container – e.g., an 8-hour day of opening and closing that container or just an hour every day).
Make sure your base coat is completely dry before writing the catalog # on the base coat. Drying time varies by geographic location and internal climate control (generally, more humid = longer drying time). After your base coat is completely dry (meaning it is hardened), then write the catalog #. Make sure the ink is completely dry before applying the top coat. I prefer the Sakura Pigma Micron artists pens over the Faber-Castell Pitt pens for labeling catalog #s on B-72.
Some of the reasons why hand-written ink will smear, run, or “disappear” are: (1) the base coat and ink were not completely dry when the top coat of B-72 was applied, or (2) the item being labeled is slightly more porous and requires a second base coat of B-72 (applying one base coat, letting it dry completely, then applying a second base coat on top of that to dry completely, then label, then a top coat).
As for labeling catalog #s on dark items, if you opt for using a separate white acrylic (water-based) as a background color, be sure to put down a base coat of B-72 before the coat of acrylic. However, you can also purchase B-72 with a white acrylic already mixed into it from University Supplies. If you don’t like the appearance of that, you can purchase white ink to write the catalog # on dark items. We use Koh-I-Noor Drawing Ink in white (and a quill pen).