LAKES.
Organic colouring matters for use as pigments are mostly made in the
form of “lakes,” by one of the three following methods:--
(_a_) To a filtered solution of the colouring matter is added a
solution of alum; the whole is agitated, and the colour is precipitated
by a solution of carbonate of potash.
(_b_) A solution of the colouring matter is made in a weak alkaline
lye, and precipitated by adding a solution of alum.
(_c_) Recently-precipitated alumina is agitated with a solution of the
colouring matter as before, until the liquid is nearly decolorised,
or the alumina assumes a sufficiently deep tint. The first method is
generally adopted for acidulous solutions of colouring matter, or those
injured by alkalies; the second for those not injured by alkalies; the
third, for those whose affinity for gelatinous alumina enables them to
combine with it by mere agitation.
Alumina in a state suitable for the preparation of the pigments known
as “lakes” may be produced in the following manner:--Dissolve 1 lb. of
alum in ½ gallon of water, and add 75 grains of sulphate of copper,
and about ¼ lb. of zinc turnings; leave the mixture for three days in
a warm place, renewing the water lost by evaporation. The copper is
first deposited upon the zinc, the two metals thus forming a voltaic
couple sufficiently strong. Hydrogen is disengaged, sulphate of zinc
is formed, and the alumina gradually separates in the state of a
very fine powder; the action is allowed to continue until there is
no more alumina left in solution, or until ammonia ceases to give a
precipitate. If the reaction is prolonged beyond this point, oxide of
iron will precipitate if present. The alumina washes easily, and does
not contract upon drying.
BRAZIL-WOOD LAKE.--(_a_) Digest 1 lb. ground Brazil-wood in
4 gal. water for 24 hours, boil ½ hour, and add 1½ lb. alum dissolved
in a little water; mix, decant, strain, add ½ lb. tin solution, again
mix well, and filter; to the clear liquid cautiously add a solution of
carbonate of soda while a precipitate forms, avoiding excess; collect,
wash, and dry. The shade will vary according as the precipitate is
collected.
(_b_) Add washed and recently-precipitated alumina to a strong filtered
decoction of Brazil-wood.
CARMINATED LAKE.--(_a_) The cochineal residue left in making
carmine is boiled with repeated portions of water till exhausted;
the liquor is mixed with that decanted off the carmine, and at once
filtered; some recently-precipitated alumina is added, and the whole
is gently heated, and well agitated for a short time. As soon as the
alumina has absorbed enough colour, the mixture is allowed to settle,
the clear portion is decanted, and the lake is collected on a filter,
washed, and dried. The decanted liquor, if still coloured, is treated
with fresh alumina till exhausted, and thus a lake of second quality is
obtained.
(_b_) To the coloured liquor obtained from the carmine and cochineal
as just stated, a solution of alum is added, the filtered liquor is
precipitated with a solution of carbonate of potash, and the lake is
collected and treated as before. The colour is brightened by addition
of tin solution.
CARMINE.--Boil 1 lb. cochineal and 4 dr. carbonate of potash
in 7½ gal. water for ¼ hour. Remove from the fire, and stir in 8 dr.
powdered alum, and allow to settle for 20 to 30 minutes. Pour the
liquid into another vessel, and mix in a strained solution of 4 dr.
isinglass in 1 pint water; when a skin has formed upon the surface,
remove from the fire, stir rapidly, and allow to settle for ½ hour,
when the deposited carmine is carefully collected, drained, and dried.
COCHINEAL LAKE.--(_a_) Digest 1 oz. coarsely powdered
cochineal in 2½ oz. each water and rectified alcohol for a week;
filter, and precipitate by adding a few drops of tin solution every 2
hours, till the whole of the colouring matter is thrown down; wash the
precipitate in distilled water, and dry.
(_b_) Digest powdered cochineal in ammonia water for a week; dilute
with a little water, and add the liquid to a solution of alum as long
as any precipitate (lake) falls.
(_c_) Boil 1 lb. coarsely powdered cochineal in 2 gal. water for 1
hour; decant, strain, add solution of 1 lb. cream of tartar, and
precipitate with solution of alum. By adding the alum first and
precipitating the lake with the tartar, the colour is slightly changed.
MADDER LAKE.--(_a_) Tie 2 oz. madder in a cloth, beat it well
in a pint of water in a stone mortar, and repeat the process with about
5 pints of fresh water till it ceases to yield colour; boil the mixed
liquor in an earthern vessel, pour into a large basin, and add 1 oz.
alum dissolved in 1 pint boiling water; stir well, and gradually pour
in 1½ oz. of strong solution of carbonate of potash; let stand until
cold, pour off the yellow liquor from the top, drain, agitate the
residue repeatedly in 1 qt. boiling water, decant, drain, and dry.
(_b_) Add a little solution of acetate of lead to a decoction of
madder, to throw down the brown colouring matter; filter, add solution
of tin or alum, precipitate with solution of carbonate of soda or
potash, and proceed as before.
(_c_) Macerate 2 lb. ground madder in 1 gal. water for 10 minutes;
strain and press quite dry; repeat a second and third time, and add
to the mixed liquors ½ lb. alum dissolved in 3 qt. water; heat in
water-bath for 3-4 hours, adding water as it evaporates; filter first
through flannel, and when cold enough through paper; add solution of
carbonate of soda as long as precipitate falls; wash the latter till
the water comes off colourless, and dry.
YELLOW LAKES.--(_a_) Boil 1 lb. Persian berries,
quercitron-bark, or turmeric, and 1 oz. cream of tartar, in 1 gal.
water till reduced to half; strain the decoction, and precipitate by
solution of alum.
(_b_) Boil 1 lb. of the dyestuff with ½ lb. alum in 1 gal. water, and
precipitate by solution of carbonate of potash.
(_c_) Boil 4 oz. annatto and 12 oz. pearlash in 1 gal. water for ½
hour; strain, precipitate by adding 1 lb. alum dissolved in 1 gal.
water till it ceases to produce effervescence or a precipitate; strain
and dry.
For information concerning the numerous coal-tar colours now largely
manufactured into lakes, the reader is referred to “Spon’s Encyclopædia
of Industrial Arts.”