How I label a vial so the label survives the freezer

I once found a label at the bottom of a freezer box. Just the label. It was neatly written, with a batch number and a date, and it had come off one of nine identical vials standing above it. All nine were bare glass with a grey stopper. None of them was offering to say which one it belonged to.

That box taught me more about labelling than any guideline. Since then I think of the label as a piece of equipment, with its own ways of failing, and I pick it as carefully as I pick the box.

How labels fail

There are three ways, as far as I can tell, and I have met them all.

The first is glue. Ordinary office labels are made for paper at room temperature. On cold glass the adhesive goes hard, loses its grip and lets go at the edges. A vial that is taken out, handled with gloves and put back a few times will shed that label sooner or later, usually into a box where it can do the most damage.

The second is ink. Some markers that look permanent on paper turn out to be mere suggestions on a glossy label. One wipe with a glove that has touched ethanol and the batch number becomes a blue cloud. Ballpoint is worse in a different way: it doesn’t write on a cold surface at all, so people press harder, tear the label and give up.

The third is water. Every time a cold vial meets room air, a film of condensation forms on it. Paper drinks that film. After a dozen outings the paper swells, the fibres lift and the writing sinks into a soft grey mush. It happens slowly, which is the annoying part. The label is perfectly legible on the day you check it and useless three months later.

What I use now

Labels sold for low-temperature storage. They are thin plastic rather than paper, the adhesive is rated for the freezer, and they cost a bit more than the office kind. A sheet lasts me a long time, because vials are small and I don’t have that many.

The pen is a fine-tipped solvent-resistant marker, black. Not blue, not red, not whatever happens to be lying next to the balance. Black on white reads well through frost and through a scratched box lid. I keep two of them tied to the freezer handle with a piece of string, which looks ridiculous and has saved me a great many walks across the room.

I tested the combination before trusting it, in the least scientific way imaginable. I labelled three empty vials, wrote on them, left them in the freezer for a fortnight and then rubbed each one with a gloved thumb, a damp tissue and a tissue with ethanol. Two markers survived all three. One didn’t survive the thumb. That one now lives in a drawer with the paper labels, where they can keep each other company.

The order matters

I write the label first and stick it afterwards. Writing on a flat sheet is easy. Writing on a curved vial the width of a finger, while holding it with the other hand, produces handwriting I can’t read myself.

And I label at room temperature, on dry glass, before the vial goes into the cold. An adhesive that holds beautifully at −20 °C still needs a clean, dry surface to grab in the first place. If a vial arrives already chilled and misted, I let the mist go, wipe the glass dry and only then put the label on. Sticking a label onto a wet vial is a way of scheduling a problem for later.

The label goes around the body of the vial, low down, with the ends overlapping slightly if it is long enough. A label that wraps onto itself holds far better than one relying on glass alone. I leave a vertical window of bare glass so I can still see the powder inside without peeling anything.

What goes on it

Very little. A vial offers about as much writing space as a postage stamp, so every character has to earn its place. Mine carry four things:

• a short name for the compound, the one used in the logbook;
• the supplier’s batch number, copied character by character;
• the date the vial arrived;
• my own running number, which is the line in the logbook.

The running number is the one I would keep if I could keep only one. Everything else about the vial sits in the notebook under that number: who supplied it, which papers came with it, where it is stored, when it was taken out and why. The label is a pointer, the notebook is the record.

I don’t cover the manufacturer’s label, if there is one. It stays visible and mine goes beside or below it. If the two ever disagree, I want to be able to see both.

The second label

Since the day of the orphan label I mark the cap as well. A small round sticker on top of the flip-off cap, with the running number and nothing else. It does two jobs. When I look into a box from above I can find a vial without lifting out the whole row. And if a body label fails in spite of everything, the cap still says which line in the logbook to open.

Caps can be swapped, of course, so I don’t take the dot as proof. It is a second chance, and second chances are cheap at this price.

The nine bare vials

They are still in the logbook, as a single line with a note beside it. I knew the batch from the label on the floor of the box, and all nine had arrived together, so in principle the label fitted any of them. In principle. One of the positions in that box had been refilled at some point, and I couldn’t rule out that the newcomer was among the nine. So the note reads “identity not confirmed, not for use”, and the vials moved to a separate box with a red lid.

Once a quarter I open the freezer with a list and do nothing but read labels. Any vial whose writing has started to pale gets a fresh label next to the old one, never on top of it, and the logbook gets a line saying so. It takes twenty minutes and a pair of thick gloves. The red-lidded box sits on the top shelf where I see it each time, which is the only reason I keep it.