GLASS IV. Of green colours.
ERDIGRÏSE is a raft or corrofion of copper formed by the adtion of fome vegetable acid, commonly that of the fkin and pulp of grapes remaining after they
have undergone a preflure for wine. It is brought from Italy hither; and ufed in moft kinds of painting, where green is required.
Verdigril'e makes a blue green colour in paint: bjut is generally ufed with yellow, which by a proper mixture renders it a true green. It is bright when good ; but very foon flies when ufed in oil: but when ufed in water painting it is diflolved previoufly in vinegar; which, in-deed, changing it to another fubftance, renders it more durable.
It is needlefs to give any procefs for the making verdigrife; becaufe it may be pur- chaled much cheaper than it can be here made: the preffings of the grapes in countries where
Of verdigrife.
much wine is made faving the expence of the acid; which as it mud be vinegar could not be procured here without coll: thefe preflings are rubbed on plates of copper, which are then put in moill places, till a ftrong corrofion or ruft is formed, which beaten or fcraped off is the verdigriie.
There is no other preparation of it neceflaiy to the ufing verdigriie in oil or varnifh, except a fufficient levigation; but in water painting, as is faid before, it mud be diflolved in vinegar; ■when in fadt it ceafes to become verdigrife, and is a lalt of copper; the lame with the chryllals of verdigriie we lhall next treat of.
Solution in vinegar is not, however, the only method by which verdigriie may be ufed in water painting: for it will diflolve in the juice of rue; and produces a fine full green colour equally fit for walhing with that diflolved in vinegar.
The goodnefs of verdigriie may be diltin- guilhed by the fulnefs of its blue green colour, and inclining rather towards a chryftalline texture than the form of a powder j to which mull be added its being free from feculencies,
Chryjials of verdigrife, called diftilled verdigrife,
Diftilled verdigrife is the fait produced by the lolution of copper, or common verdigrife, in vinegar. The chryllals thus formed are of an extreme bright green colour; and in varnifh, where they Hand perfectly well, they have a very fine effeft. In oil they hold their colour well enough to anfwer many purpofes, where colours are not required to be greatly durable ; but in paintings of confequence they cannot be depended upon, being apt to turn black with time.
The chryftals of verdigrife may be prepared, in the following manner.
“ Take of the bed: verdigrife four ounces, “ and of diftilled vinegar two quarts. The. “ verdigrife being well pounded, let them be “ put into a circulating veflel, which may be “ formed of a mattrafs, (which is a round “ bodied glafs with a long ftrait neck) and a “ Florence flafk, which muft have its neck “ inverted into the mattrafs, the thick end be- “ ing broken off. This circulating veflel muft “ be placed in a gentle fand-heat, or other “ warm fituation, where it muft continue, “ being frequently fhaken, till the vinegar has “ diflolved as much as it can of the verdi- “ grife. Remove the verdigrife and vinegar “ then into a proper glafs for decanting the “ fluid, when it fhall become clear, from “ the fediment: and when it has flood a due “ time to fettle, let it be carefully poured off <{ and evaporated to about half a pint j which “ may be beft done with a fand-heat, in a “ glafs body or cucurbit, having its neck cut
off to form a wide mouth. It may be fet “ to flioot in the fame veflel or in a glafs “ receiver with a wide neck : and, when “ the chryftals are formed, they muft be
“ taken
“ taken out, and carefully dried in the “ fhade.
“ A frefh proportion of vinegar may be <c added to the remains of the verdigrife,
“ which the firft quantity left undiffolved ;
“ and the mothers or fluid remaining after the chryftal6 were formed may be put into “ it: when, the other parts of the procefs be- “ ing repeated, a fecond quantity of the chry- “ Hals will be obtained.”
The diftilled vinegar produces the moft % beautiful cbryftals of verdigrife j but common vinegar ie more frequently ufed by thofe who prepare them: as it is much cheaper, and will afford very good coloured chryftals, if care be taken in the evaporation not to fuffer any part of it to burn to the glafs; to avoid which accident, it is proper, that the veffel, in which the evaporation is made, fhould not be funk deep in the fand ; but only let upon it, or fur- rounded a little above the bottom.
The goodnefs of the diftilled verdigrife may be perceived by the clearnefs of the chryftals; and the bright green colour of them when powdered.
Offap green.
Sap green is the concreted juice of the buckthorn berries expreflied from them.
It is a yellow green; and only ufed in water painting; where it is very ufeful for feme purpofes as a wafhing colour; making a ftrong
ftain,
ftain and pretty bright. It may be prepared
in the following manner.
“ Take any quantity of buckthorn berries “ before they be ripe ; and prefs out the juice <{ in fuch a prefs as is ufed for making cyder “ or verjuice; or by any other method. “ Strain this juice through flannel, and then “ let it Hand to fettle; and, when it has “ flood a proper time, decant off the clearer <c part of the fluid from the fediment. Put “ this juice into a ftone or earthen veflel j and " evaporate it till it begins to grow of a thick “ confiftence j then put it into the pewter “ veflel defcribed p. 24 j and, finifli the eva- “ poration in balneo mariae; collecting the “ matter into one mafs as it acquires a pro* “ per confiftence.”
The marks of goodnefs in fap green arc the tranfparency, brightnefs, and ftrength of colour, it appears to have when rubbed on
TruJJian green.
Pruflian green is the fame with the Pruflian blue ; except that in the preparation the precipitated oker of the vitriol is fuffered to remain with the precipitated earth of alum and the fulphur of the coal j the addition of the fpirit of fait, by which in the regular procefs for the Pruflian blue the oker is rediflblved, being omitted : and this oker being yellow, a green is produced by it through the effedt 1 of
of the blue of the fulphur. The qualities of the Pruflian green are much the fame • with thofe of the blue, except the difference of colour, and that it is not fo tranfparent; nor, with regard to any I have hitherto feen, fo bright j neither can it be fo well depended upon for ftanding as the Pruflian blue when well prepared, though it is nearly equal in that point to the common. As the qualities are fo much the fame, the ufes to which the Pruf- fian green may be applied are much the fame with thofe of the blue, excepting difference of hue ,; and at one time this colour was gaining ground among painters of fome kinds: but it has fince then been negledted; and at prefent feems almofl wholly laid afide, tho’ I am not fenfible of the reafon why this pigment might not be of advantage in many kinds of painting, as well as the common Pruflian blue.
The manner of preparing this pigment may be as follows.
“ Proceed in all points, as in the procefs “ given for the Pruflian blue, till the folu- “ tion of alum and vitriol be mixed with “ that of the pearl-afhes and fulphur of the “ coal, and the green precipitation made : “ then, inflead of adding the fpirit of fait, “ omit any further mixture, and go on to “ wafh the fediment, which is the Pruflian “ green; and afterwards to dry it, in the *s fame manner as is directed for the blue.”
The goodnefs of the Pruffian green confifts in the deepnefs and brightnefs of the colour $ and the more it is of a true teint of green, the better it is.
Terra verte.
Terra verte is a native earth, which in all probability is coloured by copper. It is of a blue green colour, much of that teint which is called fea-green. What we have in com«* mon' here, is not very bright, but being femi- tranfparent in oil, and of a ftrong body in water, and Handing equally well with the beft pigments, it is very much adapted to anfwer fome purpofes in both kinds of panting} though it is not fo generally ufed by thole to whom it would be ferviceable as it merits. Mr. D’Acofta fays, in his book of Foffils, that there is a kind which is very bright, and is found in Hungary: if it could be procured here, it would certainly be a very valuable acquilition to oil painting} as the greens we are forced at preient to compound from blue and yellow, are feldom fecure from flying or changing.
Terra verte, as brought from abroad, is of a very coarfe texture} and requires to be well levigated, and walhed over: but no other preparation is necefiary previoully to its ufe, The only method of diftinguilhing its goodnefs is by the brightnefs and ftrength of its colour.