Not to be confused with Printer Ink, which is almost as good and thousands of times more expensive.
Ink is a liquid with a strong colour used for writing and printing. It can turn invisible whenever it detects that you have a term paper or other important document to print.
Ink was traditionally extracted from octopussies, who use it to camouflage their nests, feed their young and annoy people who snorkel. The importance of ink in an increasingly literate society made the octopussies highly valuable, and they were even used as currency in some parts of the world, most notably Japan. Large octopus farms were constructed to handle the ever-increasing demand, and many families living by lakes, rivers or the sea kept an octopus as a pet to remain self-sufficient in times of war.
Apart from that, an old legend states that in old times, people carried cows with them. As the story told, beef was yet another great ink producer. Of course, this is nothing more than a myth and is yet to be proven.
Currently the United States government have invested millions of dollars in scientific grants to try and make this a fact. This is the kind of logical thinking and cost benefit analysis that guides government allocation of taxpayer monies.
The Ink Scare of the 1740s
The octopussies (also known as octuplets or fat squids) struggled to adapt to their new role. The constant milking for ink made them unable to properly conceal their young from predators, and by the early 1740s they were on the brink of extinction. The "black gold" or "Texas tea" dwindled ever faster.
Not much is known of this period, since few people were willing to spend ink documenting it. The acute need for ink led to the invention of alternative sources, including a synthetic ink known as soy sauce, containing equal parts of water, corn starch and darkness, and the pencil, facilitating ink-less writing for the first time since the chisel.
The pencil won out for hand writing, due to its low cost and beneficial educational impact of lead chewing. Soy sauce was reserved for formal letter-writing, and masking the taste of bad fish.
In recent years, organic ink has been produced as a luxury product by a small number of independent farmers. It's produced by training the octopuses to ink into a machine which will then give it some food based on the amount of ink squirted. This allows the octopus to only give away its surplus ink, avoiding the aforementioned problems.
Green scientists are working on a way to mix ink with hemp, thus demonstrating it's not easy being green. This would form a sticky and hairy compound that you can write, wear and smoke, potentially at the same time.
This ink comes in a variety of colours such as yellow, pink and green. It is invisible to the naked eye, and semi-translucent to the partially-clothed eye.
If you want to find out what someone has written in invisible ink, you can iron over it to reveal the words, which has the added benefit if removing unsightly creases. You can also iron over the head of the person until they tell you what they wrote, but this may increase unsightly creases.
Over 40% of all ink manufactured is indeed poisonous, and as such is valuable for writing gossip columns. Most of this ink is kept at the back of office supply cupboards, the strategic placement of this ink weans out anyone who may be stealing the office supplies.
There have been many documented cases of poisonous ink being used as a murder aide. In almost all these cases an innocent man has been accused, and as such Ms. Marple is almost always flown in by helicopter to oversee all investigating. Poisonous ink is made from regular ink mixed with cyanide. The cheapest place to get poisonous ink is in Russia, as they use it do colour paper airplanes which are flown to Ukraine.