(and yes, once again I shall substitute the short s for the long, for the sake of clarity)
(graphic of pointing hand) If you soak the green Peelings of Walnuts (at the Time of the Year when pretty ripe) and Oak Saw-dust, or small Chips of Oak, in Rain Water, and stir it pretty often for a Fortnight: the Water strained off and used with same ingredients as above, will render the Ink still stronger and better.
Or you may dissolve half an Ounce of Gum Senega, or Arabic, in Half a Pint of Water ; then put a Pennyworth of Vermilion into a small Gallipot, and pour some of the Gum Water to it, stir it well, and mix it together with a Hair-Pencil*, to a proper Consistency ; but it will not incorporate presently, tho' by the next Day it will ; then having a clean Pen, dip it into the Ink, having first well stirred it with a Pencil, and then you may use it : It is a fine and curious Red, tho' not so free as the other. And after the same Manner you may make any other coloured Ink, as Blue, Green, Yellow, Purple, &c. having divers Gallipots for that Use. In like Manner you may mix the Shell-Gold for curious Occasions ; pouring two or three Drops, according to the Direction, into the Shell, and mix it well with a clean Hair-pencil, and with it put a little into a clean Pen, &c.The small Shells may be bought at some Fan-sellers, or Fan-painters, at two or three for Two-pence ; or the large ones (which are the best) at the Colour-shops, at Six-pence a-piece.
First, If you dip your Pen in the Juice of a Lemon, or of an Onion, or in your own Urine, or in Spirits of Vitriol, and write on clean Paper whatever you intend, it shall not be discerned till you hold it to the Fire, and then it will appear legible. and if with any of the aforementioned, you write on your Skin, as on your Arm, and Back of your Hand, &c. it shall not be seen till you burn a Piece of Paper, and with the Ashes rub on the Place, and then it will appear very plain : And this I have experienced and tried, and therefore can say, Probatum est.
Another Way is, when you write a Letter that you intend it shall not be discovered, but to those you think fit ; first to write your Thoughts on one Side of your Letter with black Ink, as usual, (but it ought to be on thin Paper) and then, on the contrary side, go over the said Matter that you would have secret, with a clean Pen dipped in Milk, and that Writing shall not be read without holding it to the Fire, as mentioned above, and then it will appear legible in a bluish Colour.
A third Method is, to have two Pieces of Paper equal in Size, and the uppermost cut in chequered Holes or Squares big enough to contain any Word of six or seven Syllables, and in those Squares write your Mind in regular Sense ; and then take off the said chequered Paper, and fill up the Vacancies with Words of any Kind, which will render it perfect Nonsense, and not capable of being read, to any Purpose of Intelligence. And transmit and send the said uppermost, or chequered Paper, or another exactly of the same Form to your Correspondent ; whereby he shall, by laying it nicely on your said Letter, read your intended Sense, without being perplexed with the Words of Amusement intermixed, which make it altogether unintelligible.
Or again, you may write to your Friend in proper Sense with common Ink, and let the Lines be at so commodious a Distance, that what you intend to be secret may be written between them with Water, wherein Galls have been steeped a little Time, but not long enough to tincture the Water ; and, when dry, nothing of the Writing between the said Lines can be seen ; but when it is to be read, you must, with a fine Hair-pencil dipped in Copperas-water go between the said Lines, and so you make it legible.
Note. This Way will give you no Ground for Suspicion, because the letter seemeth to carry proper Sense in those Lines that are set at a proper Distance.
*Pencil: "an artist's paint-brush of camel's hair, sable, fitch, or other fine hair, gathered into a quill; esp. one of small and fine make, suitable for delicate work." The other kind are called 'pencils of black lead', 'dry pencils', or 'wooden pencils'.