By means of a dye process known as the "Primuline Process," very
pretty images in various colored dyes can be made upon silks, satins,
cotton goods, etc. The material is first dyed in a hot solution of
primuline, made by adding about 15 to 30 grains of the dye to a gallon
of hot water; a little common salt should also be added. On immersing
the fabric, and stirring it about in the solution, it becomes of a
primrose yellow color, when it is removed and washed under a
cold-water tap. The next process is to diazotize it by immersion for
half a minute or so in a cold solution of sodium nitrate, one-quarter
per cent., which has been sharply acidified with hydrochloric or other
acid. The material is again washed in cold water, but it must be kept
in a weak light. It can be hung up to dry, in the dark, or exposed
while wet beneath the object of which it is required to produce a
positive reproduction. This process gives a positive from a positive,
so that any ordinary picture on a sufficiently translucent
material--flowers, ferns, etc.--can be reproduced. Printing requires
about half a minute in the direct sunlight to half an hour or more in
dull weather, or if the material to be printed through is not very
transparent. The high lights become of a pale yellow, so that a faint
image is perceptible; but this is made visible in almost any color by
development in a weak solution (about one-fourth per cent.) of a
suitable phenol or amine. The following have been found suitable:
_For Red._--An alkaline solution of [Greek: b]-napthol.
_For Maroon._--An alkaline solution of [Greek: b]-napthol-disulphonic
acid.
_For Yellow._--An alkaline solution of phenol.
_For Orange._--An alkaline solution of resorcin.
_Brown._--A slightly alkaline solution of pyrogallol, or a solution of
phenylene-diamine-hydrochloride.
_For Purple._--A solution of [Greek: a]-napthylamine hydrochloride.
_For Blue._--A slightly acid solution of amido-[Greek:
b]-napthol-sulphonate of sodium, now better known as "eikonogen."
If the design is to be made in several colors, this can be done by
painting on the different developers, suitably thickened with starch.
After developing, the material is well washed and dried. With the
purple and blue developers it is necessary to wash the material
finally in a weak solution of tartaric acid. Wool and silk require a
longer exposure to light than other fabrics, and cannot be
successfully developed with the maroon or blue developer.