Dictionarium polygraphicum. [Glass, painting.]

Dictionarium Polygraphicum:
Or, The Whole Body of Arts Regularly Digested.
Vol I.
London: Printed for C. Hitch and C. Davis in Pater-noster Row, and S. Austen in St. Paul's Church Yard. MDCCXXXV.
1735
To make white ground for painting on glass.
Now to pursue our work, we will begin with the preparation of all the colours to be used in painting glass; for before we proceed to prescribe the rules how to work, the materials must be considered.
The white is compounded of several ingredients; the first are small white river pebble-stones heated red hot over a fire in an iron ladle, and thrown afterwards into an earthen dish full of cold water to calcine them; and this must be repeated several times until they be prepar'd; afterwards being dried, pound them with a stone or glass pestle in a stone mortar, and so grind them upon a marble to an impalpable powder; then mix a fourth part of nitre with it, and calcine them in a crucible; then pound and grind them again, and calcine them a third time over a smaller fire than your former, and so take them off for use.
This done, when you would paint with it, add equal parts in weight of gyp, a sort of talk found amongst plaster mold baked on the coals to a whiteness, and reducible to powder, and rocaille, (see ROCAILLE) grind them all three well together in a hollow plate of copper with gum arabick water. Thus you'll have your white in good condition to paint withal.

To prepare black for painting on glass.
As this colour cannot be omitted in any sort of painting, so in this, the manner of using it is much the same, and the preparation easy.
You must grind scales of iron from the smith's anvil-block for three hours on the shallow copper bason or plate; add to this one third of the same weight of racaille, with a little calx of copper, to hinder the iron from turning red in the fire; grind it to as impalpable a powder as you can bring it to, and so keep it in a close vessel for use.

To prepare a yellow paint for glass.
This colour requires a more costly preparation than the precedent, because it cannot be well done without a tenth part of prepar'd silver, as is shewn hereafter.
Take fine silver in plates or leaves, stratify them in a crucible with powder of sulphur or nitre, the first and last lay being of the powder, and so calcine them in a furnace; this done, cast it out as soon as all the sulphur is consumed into an earthen bason of water, and afterwards pound it in your stone mortar until 'tis fit for the marble, and so grind it with some of its water wherein it was cooled for six hours; then add nine times its weight of red oker, and grind them together for a full hour and it's done, and fit for painting on glass.

To make a blue for painting glass.
The whole secret of this preparation depends on the calcining the ingredients, and goodness of the crucible.
Take two ounces of zaffer, two ounces of minium, and eight ounces of very fine white sand; put all these into a bell-metal mortar, and pound them very well, and so into a crucible covered and luted over a quick fire for an hour; then draw out the crucible, and pound them again as before; this done, add 3. fourth of its weight in salt-petre powdered, and having mixt als very well together, return them into a crucible covered and luted, which place again in the furnace for two hours at least, continuing such another fire as the former. The crucible being off, and cooled a second time, grind the mass as before, and so put it into a crucible again, with a fixth part of salt-petre, and let it remain on the fire for three hours; then take off the crucible immediately with an iron spatula red hot, and take out the matter left it should stick, being very clammy and hard to be emptied.
'Tis convenient to have strong crucibles for this calcination, because it remains so considerable a while in the fire, and they must be luted with an extraordinary lute, adding powder of borax to the powder of glass vitrified, which helps the fusion of the glass which we have omitted there; but the greatest stress lies in baking the crucible afterwards in a small fire to cement the pores, and make the earth compact as glass, which would be very much furthered if you would throw on it a considerable quantity of salt as it comes out of the fire. This would glaze it, and capacitate it for retaining the spirits in the fire.

To make a red colour for glass paint.
This requires as much caution as the blue.
You must take scales of iron and litharge of silver of each a dram, feretto of Spain half a dram, rocaille three drams and a half; grind all these for half an hour on a shallow copper plate; in the mean time, pound three drams of blood-stone in an iron mortar, and add it to the rest; then pound a dram of gum, arabick in that mortar to an impalpable powder to take off the remains of the blood-stone, and so add it to the rest, grinding them still continually, left the bloodstone be spoiled.
The best manner of grinding these is to pour water by little and little on the ingredients as you grind them, neither wetting them too much nor too little, but just as much as will keep a good temper, as for painting; afterwards put all into a foot glass, and so drop on it through a small hollow came of wood or with your finger, as much water as will bring it to the consistence of an egg's yolk butter'd, or a little more; then cover the glass to preserve it from dust, and so let it stand three days to settle.
After this, decant the clearest and purest of the colours that rise at the top into another glass, without disturbing the sediment; and two days after it has settled anew, pour off again the purest of the colours as before.
This done, set it in the body of a broken mattress or bolt-head over a gentle slow fire to dry easily, and so keep it for use.
When you have occasion for it, take a little fair water in a glass, and with it, moisten as much colour as you think convenient; that will be excellent for carnation. As for the fæces which are very thick, dry them too, and you may moisten these in like manner with water for drapery, timber colour, and such other as you think convenient.
It is true all painters of glass don't use these colours thus prepar’d, there being few artists of that kind, who have not invented their own particular colours, which they esteem as great secrets.
But nevertheless they that have been above describ'd are sufficient for the best paintings of all sorts, provided the workman has but the skill to manage them.

To make a purple colour for painting of glass.
The preparation of this purple colour is exactly like that of the blue, for this reason we need not use any tedious repetitions.
You must take an ounce of zaffer, and an ounce of very pure and clear perigueux, two ounces of minium, eight ounces of very fine and white sand; pound all these in a bell-metal mortar, and reduce it to an impalpable powder; put it afterwards into a good crucible well covered and luted in the furnace; keep a very good fire to it for an hour; then draw it out, and as soon as it is cold, pound the mass over again in the same mor tar; to this add a fourth part of its weight of nitre; mix them together, and put them into a crucible, and so proceed until you have a fine purple colour.

To make a green paint for glass.
The change of the ingredients makes this colour, but the method for incorporating them is the same as the former.
Take two ounces of æs ustum, to this add two ounces of minium, and eight ounces of very fine white sand; pound these together in a metal mortar to an impalpable powder, and put it afterwards in a crucible luted and covered into a wind furnace, giving it a good fire for an hour; after this, draw it off, and let it cool; then pound it again, adding a fourth part of its weight of nitre in powder; grind and mix them well together, putting them afterwards into crucible luted and covered in the furnace for two hours, and then you'll have a very fine green.

Of other colours in general for painting of glass.
We have directed how to make the first master-colours for painting on glass; now we proceed to shew what other depend on them without enlarging on these preparations.
The red serves for carnation, but there ought to be one part of feretto of Spain in the composition, and another of rocaille; grind these on your copper plate, imbibing the powder with gum'd water until it be made fit for use.
The red fæces there also mentioned will serve in drapery; and to describe timber work, trunks of trees, hair, brick and such other things, you must take an ounce of feretto of Spain as in the former composition, an ounce of iron scales, and two ounces of rocaille; grind them together on the copper plate, moistening them with gum water till they be brought to a proper consistence, neither too thick nor too thin; so you'll have a red inclining to a dark yellow, very fit for use.
There be several more made use of in this, as well as in other painting, but are compounded of the principal colours as we have intimated in our discourse of colours for painting on enamel.

Another way to paint on glass.
Take very white Glass varnish it very thin on one side with a white varnish; then having made choice of some fine impress cut on paper just fit for the piece of glass you design to paint on, dip it in water, and letting it soak and dry a little, clap the picture side thereof to the varnish side of the glass, as exactly plain and even as possible, and so let it dry thoroughly; afterwards moisten the paper on the blank side, and with a blunt graver, draw off and trace the lines of the picture, which will afterwards remain perfectly and distinctly on the varnish side of your glass quarre.
This draught is for the model; you must paint your filings in it, and observe that the tracings and strokes of the picture are to serve you in shadowing, which cannot be repeated without disadvantage to your piece.
The manner of painting on glass is quite contrary to that of limning or painting on cloth or wood; for in this, the paint being but on one side, is plainly visible on the other. Here the settings off are first done; then the compound colours just run over, and so continuing until perfected: whereas on linen, &c. the setting off or heightenings are the last strokes, and their ground colour or first is that which we end withal, and make our last lay in all pieces done on glass.
We do not shew the way to make up the colours, nor how to mix and finish the artificial ones, for that relates immediately to the art of painting, of which you will find in several other articles, and not to this art of glass-painting; and these noted herein are the same as in the other art of painting on cloth, and not very easily prepared.
You must also paint on glass just as in miniature with water colours, laying your picture underneath it as before; and this will shew finer than if done in oyl, besides the colours dry in a moment.
Your pieces being thus done in oyl, or water colours, may receive a very additional and improving beauty by overlaying all the colours, except the ground, with leaf silver, which will appear very glorious and lively on such as are transparent, to wit, lakes, verditers.

General remarks for all colours.
The first time a new pot is put into the furnace, it always leaves some sully or foulness on the glass, which spoils the colours; for this reason they always begin to melt white glass in it first, which afterwards they pour out again into another vessel, to make common glass of it. This the workmen very well know; but the second time, there will appear nothing of this foulness.
Particular care must be taken, that when you prepare materials for tinging glass, the most whereof are extracted from minerals, to do it in a separate furnace, or not have any vessels in it that you use for crystalline materials; for the smoke of metals and minerals, make crystal pale and uneven. The vessels or pots which serve for one colour must not be made use of for another, and every colour ought to have its own pot.
Care must also be taken not to calcine materials more than is necessary, for then they burn and are good for nothing.
As a proportion ought to be kept and minded in every thing we do, so we will here lay down some which must not be exceeded whether for fruit or colours. Notwithstanding when the workman makes any essay, if his colour be net deep enough in his mind, he may add as much as he shall think necessary, which sometimes depends on the preparation of the metals more or less calcined, and often on the fancy of the workman.
It is necessary also to be observed, that all the dose of the colouring ought not to be thrown on the melted glass at once, but at several times, and in proportion according to the quantity of it, stirring each time the materials, that they may both incor porate, and at the same prevent them from rising and running over.



How to order the GLAss in the furnace after it has been painted.

After the glass has been completely painted, and the draughts perfectly finish'd, the difficulty remains in baking the pieces, so as to give it a consistency with the glass, by penetration, which is to be done as follows:

You must work with the furnace here describ'd, and its stove made of good crucible earth, to contain all the work, which must be stratified in the following manner.

Take good quick lime well digested, powdered, and finely searced, and for the better security, let it be digested three times in a potter's furnace, and then powder and searce it; then lay it very even about half an inch thick on the bottom of the stove, and upon that a layer of pieces of broken Glass, and upon that another layer of the powder, and so another of glass, then an other of powder; the reason of making this stratification of powder and old glass is to prevent any injury from the violence of the fire, which will be very intense under the stove.

This done, upon the third bed or layer of powder, lay a layer of painted glass, and so continue to lay layer upon layer, each lay of powder and glass being evenly made until all the pieces of painted glass are put in or the stove full, and upon the last lay of glass, lay a layer of the powder somewhat thicker than the former.

Then cover the furnace with its shrowds of earth, joining and luting them well together all round with the best lute, so that it may admit of no respiration, but through the fire holes or the opening of the furnace; while you draw out the proofs or trials (by some call’d watches) which are bits of broken glass painted with the colours, and put in purely for the purpose of taking out and examining how the work goes on.

Having thus ordered the furnace, and the lute being well dried, begin to heat it gently with some charcoal on the outside of the furnace at the entrance, and so proceed by degrees, and very leisurely heightening it, left it should break the glass, or spoil the paint.

Continue this for two hours, then thrust the fire in further, and let it remain there for an hour, putting it in by little and little under the stove, where let it stand two hours longer; then increase the fire by degrees for two hours, and so continue to apply fuel till the furnace be full of charcoal, and you perceive the flame to convey it self through every hole of the cover; keep it thus violent for three or four hours, shutting the door of the furnace.

You must be very cautious and careful during the whole work from the first two hours that the fire remains at the en trance.

From time to time you must draw out some of the pieces of glass that you put into the stove for trials or watches to see if the colours be melted and the yellow be qualified. You may perceive how the work goes on by the sparkling of the iron bars under the stove.

As soon as you find the colours almost done, improve the fire with some very small billets of dry wood; these must be very small that they may be put in the more easily, smoke the less, and to make the flame inviron, reverberate over and round about the stove, which must be continued till the work is finished, which will be in twelve or fourteen hours; then let the fire go out, and the work cool of it self; then it will be finish'd, and take it out, or else it would soon burn the colours and break the glasses.