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
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 one place. It is best to hold the print so that the water runs off in the direction of the lines.
To dry the prints after washing they can be laid out flat in a moderately warm oven, or before a stove, the heat of course not being sufficient to cause the coating to peel.
To render the glue image more distinct the print should be immersed for a few seconds in an aniline dye solution, the glue taking up the colour readily. These dyes are soluble in either water or alcohol. A dye known as "magenta" is very good.
The process of coating the metal sheets must be performed as quickly as possible (about 10 seconds), as owing to the peculiar nature of the bichromated glue it soon sets, and once this has taken place it is impossible to smooth down any unevenness.
See that the negative and metal sheet make good contact while printing.