Every other failure in this chapter is mechanical. Damp is not. It arrives as a number nobody in the room can feel, it works on the whole collection at once, and by the time a card has taken water in and let it out again the paper has already moved. The good news is that the fix is mostly furniture removal, not equipment — because a damp room is almost never damp all the way through.

▸ THE QUICK VERSION

Aim for 45 to 55 per cent relative humidity. Above 65 the cards take moisture in, warp and invite mould. Below 35 they go brittle and old foil layers start lifting.

Measure at the shelf, not at the desk. A cold outside wall can read twenty points higher than the middle of the same room.

Move before you buy. Interior wall, main floor, off the ground. That is free and it beats every appliance.

Only seal a box once the number is right. A gasket lid preserves whatever air you shut in, including bad air.

Why the room is not one number

THE AIR IS THE SAME EVERYWHERE. THE SURFACES ARE NOT

Relative humidity is a ratio, not an amount. It compares the water actually in the air against the most that air could hold at its own temperature — and that ceiling drops fast as things get colder. So the air touching a cold surface has not gained a drop of water, yet its relative humidity climbs anyway, because the ceiling came down to meet it.

That single fact is what makes a damp room manageable. The air in your storage room is one number. The surfaces in it are half a dozen numbers, and the cold ones — the outside wall, the floor slab, the pipework behind the plasterboard — are where the trouble lives. Cards two feet away on an interior wall can sit in the target band while the box against the render is quietly over the line.

▸ ONE ROOM · ONE AIR · THREE READINGS

Nothing here changes the water in the air. Only the temperature of the shelf changes — and that is enough to cross the line.

One room, held at twenty degrees and fifty per cent, so the amount of water in the air never changes anywhere in the drawing. What changes is the surface the box is standing on. Because relative humidity is measured against what the air could hold at that temperature, a cooler surface pushes the reading up without a drop of water being added: at seventeen degrees the same air reads sixty per cent, and at thirteen degrees it reads seventy-eight. The dashed rule marks the practical cut-off — any surface more than about four degrees below room temperature has already taken the cards past sixty-five per cent. Nine degrees is the dew point, where the curve would reach a hundred and water would form on the surface itself.

Measure the shelf, not the house

ONE CHEAP METER, PUT IN THE RIGHT PLACE

An inexpensive digital hygrometer settles this in a day, and where you put it matters more than what you paid for it. Stand it on the shelf beside the boxes, at the same height, against the same wall. A meter on the desk is measuring the desk.

Then leave it. The reading swings through the day as the heating comes on and off, so a single glance tells you almost nothing; what you want is the highest number it saw. Most meters keep a running maximum for exactly this reason, and a week of maximums is the honest picture of the room. Damp rooms also swing seasonally — a garage or an attic can walk through forty points between February and August, which is why cards stored there curl even though nobody ever saw a bad number.

The number that ruins cards is rarely the average — it is the width of the walk. An unheated garage typically swings something like forty points between seasons, which drags the collection across both lines twice a year and puts a bow in everything. A closet on an interior wall of a heated floor usually stays inside a dozen or so points.

Seal, buffer, or move

FOUR CONTAINERS, THREE DIFFERENT JOBS

Once you know the number, the container decides how much of the room the cards get to feel. This is the part people buy backwards: they seal first, on the worst day of the year, and preserve the exact air they were trying to escape.

OPEN

Shelf or cardboard boxNo defence at all — the inside follows the room within hours. Perfectly fine when the shelf reading is already in the band, and it is the cheapest way to get there.

LID

Plastic bin, plain lidA delay, not a barrier. Air still exchanges around the rim, so the inside tracks the room a day or so behind. Useful against short spikes, useless against a wet season.

GASKET

Bin with a gasket lidClose to sealed, which cuts both ways: it keeps whatever you shut inside it. Fill it on a dry afternoon in a warm room, never on the morning after a storm.

+ GEL

Gasket bin and silica gelThe desiccant on the packet is silica gel. It is the only combination here that holds a number rather than following one — and it holds it only while the gel is dry.

Indicating gel changes colour when it is full; plain gel gives you nothing, which is why a forgotten pack is worse than none at all. Rechargeable canisters dry out in an oven or a socket and last for years. Whatever kind you use, a saturated pack is not a desiccant, it is a wet sponge sitting on your cards.

A gasket lid does not make the air good. It makes the air permanent.

The damp-room routine

IN ORDER · THE FIRST FOUR NEED NOTHING BUT THE METER

Put the meter where the cards are

On the shelf, at box height, against the same wall. Give it a full day before you believe anything it says.

Read the week, not the moment

Take the maximum it recorded, not the number on the screen. If the maximum is under 65 you have a placement job. If it lives above 65 you have a room job.

Move the boxes inward and upward

Off the floor onto a riser, off the outside wall onto an interior one, off the basement or garage onto a heated floor. This one step usually does more than everything below it.

Re-measure in the new spot

Same meter, same day-long wait. Most rooms land in the band here and need nothing else bought at all.

Seal only when the reading is right

Load gasket bins in the middle of a dry, warm afternoon, add fresh indicating gel, and write the date on the lid. Check the colour twice a year, not never.

If it has already got in

WHAT TO DO TONIGHT, AND WHAT NOT TO

Open the box in the driest room you have and look along the fore-edges of the stack rather than at the faces. A gentle uniform bow across a whole block is water; a single kinked card is handling. Musty smell with no visible bloom means the cardboard took it up and the cards may still be fine. Any grey or white fuzz on a sleeve means that sleeve comes off outside the house, not over the table.

Then dry slowly. Cards standing upright in an open box in a normal heated room for a fortnight is right; a radiator, a hairdryer or a sealed bin of fresh gel is not, because a fast one-sided dry-out curls exactly the cards you were rescuing. A warped card pressed between two boards under a modest weight loses some of its bow over a month, and none of the swelling that caused it.

Cards that have been through a wet season and back rarely return to where they started, which is worth knowing before you send anything away — graders read surface and edges on the card in front of them, not on the one you remember. The rest of this chapter is on binders and boxes; the layer directly against the card is sleeves and toploaders, and the sealed end of the story is slabs and card display.

ELSEWHERE IN BINDERS & BOXES

How to Choose a Binder That Will Not Damage the PagesSTEP 01 · BINDERS & BOXES
How to Tell an Archival Page From One That Only Looks Like OneGUIDE PENDING
How to Divide a Storage Box So You Can Find One CardGUIDE PENDING
How to Move a Collection Without Bending AnythingGUIDE PENDING

How to Store Cards in a Room That Gets Damp