Some ignorant non-collectors appear to think that airlines provide passengers with an individual barfbag for the sole purpose of disposing of masticated chewing gum. They then replace the bag in the seat pocket, in flagrant disregard for the clear instructions on most bags to hand used bags to the cabin crew.

Overworked cleaning staff often fail to detect the gum during their rushed sorties through the cabin, and the bag with its chewing gum load lurks undetected in the seat pocket.

Professional baggists are alert enough to check their swag for foreign bodies before smuggling them off the plane. But their legions of assistants - friends, relatives, office-mates - who also pick up bags and donate them to their friendly neighbourhood baggist, are not so circumspect. They grab the bag, failing to detect its unpleasant contents, and present it proudly to their baggist acquaintance as a trophy of their flight.

The baggist is, of course, far too polite to point out the flaw in the gift, so smiles grimly and adds the bag to his extras collection, vowing to exchange it as soon as possible for that 1945 green blotting-paper Aeroflot bag he has been lusting after for years.

In this way, chewing-gum laden bags enter the bagtrade in disproportionate numbers. Traders welcoming an exchanged bag into their collection are horrified to find a wad of dried latex gumming up their latest prize.

As all parents know, removing gum from a child's hair or clothing is well-nigh impossible. The same goes for prising the noxious wad from the interior of a bag without damaging the surface.

There is a solution, though. Rather than throw away your precious bag - or swapping it with another unsuspecting baggist - just pop it into the freezer overnight. The gum can then be removed easily and without further damage to the bag.

You could try this with your children too if they have gum in their hair. Certainly cheaper than a haircut.

Thanks to veteran collector David Bradford for this tip.