n the time they
require. So in this case no two negatives are the same in their required
exposure. Still, with the plates I am going to use, so wide is their
range for exposure that but few failures will be made on this score,
provided we are on the safe side, and expose fully.

Although these plates are not nearly so fast as gelatine plates, it may
surprise you to be told that working with a negative which to daylight at
this dull time of the year required an exposure of sixteen minutes, will,
I hope, give me good results in about a tenth of this time; and this I
obtain by burning magnesium ribbon.

At first the error I fell into when using magnesium ribbon was too much
concentration of light. I now never allow the ribbon, when burning, to
remain in one position, but keep it moving from side to side, and up and
down, in front of the ground glass while making my exposure; and if there
be any dense place in the negative which, as in printing, would have
required printing specially up, I allow the light to act more strongly on
that part; the result, as a rule, being an evenly and well exposed plate.

I must not forget to explain to you the manner in which I coil up the
ribbon before I set it alight. I take an ordinary lead pencil, and wind
the ribbon round and round, thus making a sort of spiral spring; this
done, I gently pull the coils asunder. I then grasp the end of the ribbon
with a pair of pincers, light the other end, and make my exposure.

Having said so much regarding exposure, I shall now proceed to deal with
development. You will see me use a canary light, with which I can easily
see to read a newspaper. It may cause some of you surprise to see me use
so much light. It is the same lamp that I use for developing all my rapid
bromide plates; it is the best lamp I ever used. The canary medium is
inserted between the two sheets of glass 71/4 by 41/2, the two glasses are
then fastened on to the tin with gummed paper, a few holes are bored in
the back for air, a funnel let in, and the thing is complete.

The formula for development is as follows:

Pyro. 96 grains.
Methylated spirits. 1 ounce.
Bromide of potash. 12 grams.
Water. 1 ounce.
Carbonate ammonia. 60 grains.
Water. 1 ounce.

Mix 30 drops pyro with from 30 to 60 drops bromide, then add 2 drachms
ammonia solution and 2 drachms of water.

I find a thin negative requires a slow development, and so gain