Another way of witches communicating with one another was to write messages, in what has come to be called invisible Ink.
One really interesting method:
Was to use an egg for the message. Which could easily be slipped to the other Witch, within a basket of eggs at the marketplace.
The Egg should be hard boiled at least 5 minutes; and cooled. Dissolve as much alum as you can in a tablespoon of vinegar. Alum is found in the pharmacy or in the grocery store with pickling supplies. Use this solution to write on the eggshell using a piece of straw from a broom, a toothpick, or a small brush.
Once the egg is dry, it looks perfectly normal. When the shell is removed, the writing is visible on the egg's surface. (Note: although alum has been used for years in pickling, it is no longer considered as safe as it once was (an the aluminum compounds may be linked to Alzheimer's Disease) so it is best not to eat too many of these eggs.
There are Two methods used:
For invisible writing on paper or parchment.
The First method, (which I feel is preferable),
Is that the writing compound is heat sensitive and becomes visible when heated. It disappears again, once the item cools. Heat sensitive invisible inks are usually fairly simple organic liquids that will appear invisible once they have dried on a sheet of paper, but will darken when held over a heat source.
Here are the directions:
Pour or squeeze approximately 2 tablespoons of lemon or
onion juice into a small bowl. Lemon or onion juice work best.
But milk or vinegar can also be used.
Dip a straw, small brush or Cotton swabs to write your
message on the paper. Let it air dry naturally, do not heat.
The dried paper is held some distance over a candle, or
pressed with a hot iron. There is, a danger of the paper
catching on fire with the candle, or scorching with the iron,
so take the necessary precautions. It will be a little smoky,
but the message should appear fairly quickly.
Prisoners used this method to sneak out messages, using
their own sweat and saliva as ink.
With the other method:
The message is written in the invisible compound and after it has dried; it is brushed with another liquid that stains the paper and the message is then revealed; either by the message being left unstained; or stained darker than the background. After the message is revealed it remains visible and needs to be destroyed.
Here are several different formulas for the Writing compound and Revealing liquid.
I Combine 2 tablespoon of baking soda and 2 tablespoon of
water in a cup. Dip a straw, small brush or Cotton swabs to
write the message on light paper. After the paper is
completely dry, you can paint over it with purple grape juice
and it will become visible.
II Use lemon juice; and a straw, small brush or Cotton swabs to
write the message. Allow it to dry. Brush a dilute solution of
iodine and water (10 or so drops in 1/4 cup (60 ml) of water).
The iodine will complex with the starch in the paper
and turn purple. The lemon juice painted sections will remain
white. Caution: Iodine is toxic and will stain almost anything it
touches brown and is not an easy stain to remove.
III Combine 1 tablespoon of cornstarch to 1/2 cup of water.
Cook until it starts to thicken. Let it cool, and write your
message. After the paper is completely dry, you can sponge it
with a solution of iodine and water (10 or so drops in 1/4 cup
(60 ml) of water). Your writing will appear in a dark blue, and
the paper will be a lighter blue.
IV Use a half cup of water and vinegar, or half cup of water
and ammonia. Dip a straw, small brush or Cotton swabs to
write the message on light paper. Allow the message to dry
completely. To read the message: spray, paint or blot with dye
solution. (Use care because the solution stains.)
For the solution: Chop red cabbage into small pieces. Boil
until the water turns a deep shade of purple. (you can also
use red Beets). Allow to cool.