nutes, depending upon the
thickness of the film. As soon as it is dry the print is ready for use.

As already mentioned, the negative from which the metal print is made
requires that the lines be perfectly sharp and opaque, and the spaces
between perfectly transparent. Ordinary dry plates are too rapid, a rather
slow plate being required. Wratten Process Plates give excellent results,
and the following is a good developer to use with them:

Glycin 15 grammes 1 oz.
Sulphite of Soda 40 ,, 2-1/2 ,,
Carbonate of Potash 80 ,, 5 ,,
Water 1000 c.c. 60 ,,

This developer should be used for 6 minutes at a temperature of 50deg F.,
3-1/2 minutes at 65deg, and 1-3/4 minutes at 80deg. It is best only used
once. If an intensifier is required, the following formula will be found to
give satisfactory results:

Bichloride of Mercury 1 oz. 60 grammes.
Hot Water 16 ,, 1000 c.c.

Allow to cool, completely pour off from any crystals, and add:

Hydrochloric Acid 30 minims 4 c.c.

Allow negative to bleach thoroughly, wash well in water, and blacken in 10
per cent ammonia .880, or 5 per cent sodium sulphide.

In preparing the negatives and metal prints the following points should be
observed:

A good negative should have the lines perfectly sharp and opaque; there
should be no "fluff" between the lines even when they are close together.

A properly exposed and developed negative should not require any reducing
or intensifying.

If the lamps used for illuminating the copying board are placed 2 feet
away, and the exposure required is 5 minutes, the exposure, if the lamps
are placed 4 feet away, will be {123} 20 minutes, as the amount of light
which falls upon an object decreases as the inverse square of the distance.

Get the coating on the foil as thin as possible, and err on the side of
over-exposure, for if the coating is thick and has been under-exposed,
excessive washing will dissolve the whole coating; for, unless
insolubilisation has taken place right up to the metal base, the under
parts will remain in a more or less soluble condition.

On no account must the unexposed sheets be placed near a fire, otherwise
they will be spoilt, the whole coating becoming insoluble; heat acting in
the same manner as light.

In washing, keep the print moving so that the stream of water does not fall
continually in o