The Primuline Or Diazotype Process

Primuline, discovered in 1887 by Mr. A. G. Green, an English chemist, is a

dye of a primrose color, possessing a great affinity for cotton fibers, to

which it is readily fixed by simply immersing the material for a few

moments in a hot solution of the dye. If the material so dyed be placed

in an acidified solution of nitrous oxide, the primuline is diazotized,

forming a derivative compound of a deeper color, which fades in the lig

and which in presence of amines and phenols gives rise to a variety of

dyes whose color depends on the reagent employed, while, when acted on by

light, the resulting compound is entirely deprived of this property. In

other words, the diazotized primuline acts as a mordant only when not

altered by the luminous action.

The chemical change light effects in the diazotized primuline is not well

known. It is pretty certain, however, that nitrogen is set free, for if

gelatine imbued with primuline be immersed in water after insulation,

nitrogen is set free and can be collected as usual in a tub filled with

water and inverted on the substance.

By itself diazotized primuline is slowly influenced by light, but quickly

acted on in presence of organic substances. It is more sensitive when

applied on cotton or paper than on wool, silk, linen, and such organic

compounds as gelatine, albumen, caseine, starch, etc. Its sensitiveness

is about one-tenth less with gelatine than with cotton.

The sensitiveness of diazotized primuline to light, when united to organic

substances and the different colors which can be obtained with the

unaltered compound, have given rise to an interesting printing method, the

invention of Messrs. A. G. Green, C. F. Cross, and E. J. Bevan, which

yields positive impressions from positive cliches. The manipulations of

the process are simple:

In a certain quantity of rain water, kept at nearly the boiling

temperature by an alcohol lamp placed under the vessel, dissolve per cent.

2 parts of commercial primuline, and in this immerse, by means of a glass

rod, some pieces of calico--free from dressing--turning them over several

times during the immersion. When the fibers are well imbued, which

requires from four to five minutes, remove the calico with the glass rod

and rinse it thoroughly in water. This done, wring out the superfluous

liquid as much as possible, and, finally, immerse each piece separately in

a solution of

Sodium nitrite, 7 parts


Hydrochloric acid, 16 parts


Water 100 parts

After turning the pieces of calico two or three times over, they are

rinsed to eliminate the acid, then drained and placed between sheets of

blotting paper to dry. All this, except the impregnation with primuline,

should be done in the dark room.

As said above, primuline is transformed by nitrous oxide into a diazotized

compound, and consequently the material is now susceptible of being acted

on by light. It does not keep, and should be exposed, etc., soon after

its preparation.

Paper is impregnated with primuline either by floating or brushing. The

best results are obtained with paper previously sized with arrowroot or

gelatine in order to keep the image entirely on the surface of the paper.

Linen, silk and wool are treated as calico.

The cliches should be positive to obtain positive expressions and somewhat

more opaque than those employed in the processes before described, else

vigor and intensity could not be obtained. Here we must state that the

primuline process seems to be better adapted for the reproductions of

drawings, such as made for the black process, and of opaque photo-cliches

in lines, or white and black, than for printing in half tone.

When the material to print upon is thick and wholly impregnated with

diazotized primuline, it is advisable, since the insulation could not be

prolonged to effect the change through, to expose the back of the material

for a certain but short period in order to clear it. This is especially

advantageous when the cliche is not of good intensity.

During the exposure, which varies from 30 seconds to 10 minutes and more

by a dull light, the progresses of the luminous action is seen by the

bleaching of the material which assumes a dingy coloration. But in order

to ascertain when the decomposition is complete on the ground of the

image, it is well to use tests as in the cyanofer process, dipping one

of them in the developer from time to time.

The developers are compounded as follows:


Beta-naphthol 4 parts

Caustic potassa 6 parts

Water 500 parts

Rub the alkali and the naphthol with a little water in a mortar and add

the remainder of the water.


Resorcin 3 parts

Water 500 parts

When dissolved add

Caustic potassa 5 parts


Carbolic acid, cryst 5 parts

Water 500 parts


Naphthylamine 6 parts

Hydrochloric acid, in 6 parts


Mix in a mortar, then add

Water 500 parts


Eikonogen, white crystals 6 parts

Water 500 parts

Pulverize the eikonogen, add the water and, at the same time, the material

on its removal from the printing frame, and keep in motion until the

development is effected.


Pyrogallol 5 parts

Water 500 parts

After the development, which requires but a few moments, it suffices to

wash the material to fix the image by eliminating the soluble compounds.

However, for purple the material should be passed in a dilute solution of

tartaric acid and not washed afterwards; it should remain acid.

When it is desirable to obtain an impression in several colors, the

various developers are thickened with starch, then locally applied with a

brush on the image, which is always visible after exposure.

For printing on wood, glass and porcelain, see further on.