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 contrast; while hard negatives are best over-exposed and quickly developed.

The plate is first placed in water or rinsed under a gentle stream from the tap till all greasiness has disappeared, it is then placed in a flat dish, and the developer applied.  Should it be found that some parts of the picture are denser printed than should be by the ribbon acting more strongly on some particular part—­this is often the case if the negative has been thinner in some parts than others, through uneven coating of the plate—­the picture need not be discarded as a failure, for I will explain to you later on how to overcome this difficulty.