Fourthly, They to save the Press-man the labour of Rubbing the Blacking into Varnish on the Inck-Block, Boyl the Blacking in the Varnish, or at least put the Blacking in whilst the Varnish is yet Boyling-hot, which so Burns and Rubifies the Blacking, that it loses much of its brisk and vivid black complexion.
Fifthly, Because Blacking is dear, and adds little to the weight of Inck, they stint themselves to a quantity which they exceed not; so that sometimes the Inck proves so unsufferable Pale, that the Press-man is forc’d to Rub in more Blacking upon the Block; yet this he is often so loth to do, that he will rather hazard the content the Colour shall give, than take the pains to amend it: satisfying himself that he can lay the blame upon the Inck-maker.
Having thus hinted at the difference between the Dutch and English Inck, I shall now give you the Receipt and manner of making the Dutch-Varnish.
They provide a Kettle or a Caldron, but a Caldron is more proper, such an one as is described in Plate 9. at m. This Vessel should hold twice so much Oyl as they intend to Boyl, that the Scum may be some considerable time a Rising from the top of the Oyl to the top of the Vessel to prevent danger. This Caldron hath a Copper Cover to fit the Mouth of it, and this Cover hath an Handle at the top of it to take it off and put it on by. This Caldron is set upon a good strong Iron Trevet, and fill’d half full of old Linseed-Oyl, the older the better, and hath a good Fire made under it of solid matter, either Sea Coal, Charcoal or pretty big Chumps of Wood that will burn well without much Flame; for should the Flame rise too high, and the Oyl be very hot at the taking off the Cover of the Caldron, the fume of the Oyl might be apt to take Fire at the Flame, and endanger the loss of the Oyl and Firing the House: Thus they let Oyl heat in the Caldron till they think it is Boyling-hot; which to know, they peel the outer Films of an Oynion off it, and prick the Oynion fast upon the end of a small long Stick, and so put it into the heating Oyl: If it be Boyling-hot, or almost Boyling-hot, the Oynion will put the Oyl into a Fermentation, so that a Scum will gather on the top of the Oyl, and rise by degrees, and that more or less according as it is more or less Hot: But if it be so very Hot that the Scum rises apace, they quickly take the Oynion out, and by degrees the Scum will fall. But if the Oyl be Hot enough, and they intend to put any Rosin in, the quantity is to every Gallon of Oyl half a Pound, or rarely a whole Pound. The Rosin they beat small in a Mortar, and with an Iron Ladle, or else by an Handful at a time strew it in gently into the Oyl lest it make the Scum rise too fast; but every Ladle-full or Handful they put in so leasurely after one another, that the first must be wholly dissolv’d before they put any more in; for else the Scum will Rise too fast, as aforesaid: So that you may perceive a great care is to keep the Scum down: For if it Boyl over into the Fire never so little, the whole Body of Oyl will take Fire immediately.
If the Oyl be Hot enough to Burn, they Burn it, and that so often till it be Hard enough, which sometimes is six, seven, eight times, or more.
To Burn it they take a long small Stick, or double up half a Sheet of Paper, and light one end to set Fire to the Oyl; It will presently Take if the Oyl be Hot enough, if not, they Boyl it longer, till it be.
To try if it be Hard enough, they put the end of a Stick into the Oyl, which will lick up about three or four drops, which they put upon an Oyster-shell, or some such thing, and set it by to cool, and when it is cold they touch it with their Fore or Middle-Finger and Thumb, and try its consistence by sticking together of their Finger and Thumb; for if it draw stiff like strong Turpentine it is Hard enough, if not, they Boyl it longer, or Burn it again till it be so consolidated.
When it is well Boyled they throw in an Ounce of Letharge of Silver to every four Gallons of Oyl to Clarifie it, and Boyl it gently once again, and then take it off the Fire to stand and cool, and when it is cool enough to put their Hand in, they Strain it through a Linnen Cloath, and with their Hands wring all the Varnish out into a Leaded Stone Pot or Pan, and keeping it covered, set it by for their use; The longer it stands by the better, because it is less subject to turn Yellow on the Paper that is Printed with it.
This is the Dutch way of making Varnish, and the way the English Inck-makers ought to use.
Note, First, That the Varnish may be made without Burning the Oyl, viz. only with well and long Boyling it; for Burning is but a violent way of Boyling, to consolidate it the sooner.