invisible ink

Last two words are written in invisible ink but can be easily discerned if Australian law books are held over scented candles.

He communicated invisible ink on postcards, and a special code of microdots.

Invisible ink makes an appearance in the complaint as does Morse Code, which, of course, is pretty uncrackable.

We always write our most secret doings in invisible ink, made of lemon juice, so that nobody can read about them.

Dip the roses in the red invisible ink, the jonquilles in the yellow, the pinks in the violet, and the leaves in the green ink.

Here for some reason the invisible ink answered less reluctantly to the warmth of the blue flames' invitation.

Our censor chaps at home have got to be quite expert at reading letters, invisible ink and all that sort of thing.

By writing in newspapers, sometimes with invisible ink or by enclosing accounts or letters in them.