The plate is prepared and exposed as in the usual method of the Daguerreotype.

A white back-ground is employed.
Let the head of the sitter come in the middle of the plate, and before exposing it to the vapors of mercury, put a small mat or diaphragm, having a small hole through it, over or directly on the surface of the plate.

This diaphragm should be bevelled, and the bevel should be towards the surface of the plate; this, in order to prevent too sharp a line on the impression.

It will be readily seen that if an impressioned plate so covered is placed over the mercury, it will be developed on such portions only as are exposed.

The principle is so familiar that further explanations are unnecessary.
NATURAL COLORS IN HELIOGRAPHY.
This subject is worthy the attention of every operator.