Heat Revealing "Ink"

[Daerir]

Wait for it....

Lemon Juice!! If you dip your pen or quill in pure lemon juice, write with it, let it dry completely. You will have a blank paper!! Place it up against something that will slowly burn the paper and you can read a hidden message!!

[Straelbora]

Now if we could just get some lemons by the pirates of Umbar.....

[armchair]

I used to do this as a kid (don't ask how long ago). According to some book I had back then, you could also use onion juice, and I think milk as well. I figured milk would stink after very long, onion juice was too much work, but Mom always had a bottle of lemon juice in the fridge.

[Daerir]

I figured heat revealing ink would be perfect for rangers who need to receive their orders from dead drops and do so without anyone knowing. Cool things we can think about

[RikJohnson]

I used to do the lemon-ink think too. totally forgot about it but it is mentioned in many books-for-boys. Another resource we overlook.

The plan for the invisible ink is to write a normal letter that will be ignored but write the message in the margins with the invisible ink. That way you could put a 'code' word in the heading to alert the recipient (often a fake name) that there is a hidden message.

I seem to recall older movies had the message accidently discovered when the good guys were trying to read aletter by candlelight and accidently overheated the parchment.

[Daerir]

I seem to recall older movies had the message accidently discovered when the good guys were trying to read aletter by candlelight and accidently overheated the parchment.

Funny you should say that, the first time I tried it, I used a match and when the flame hit the wood, it got bigger and caught my paper on fire lol

[Southwind]

I've tried milk, it works. I would think other fruit juices would also work, so maybe we can just use our local produce rather than importing lemons from Umbar. Clearly, more experimentation is called for.

[BrianGrubbs]

To use something that we know was available to them without a doubt, I've heard that potato juice also works.

Brian

[RikJohnson]

some work better than others.
Some will cause the paper toi swell and warp, others are unsuitable for writing. Milk isn;t as good as lemon juice as it turns rancid and you can smell the stink after a few days.
It's just a matter of testing everything like:

"I wrote this with lemon juice on 14 November"

"I wrote this in milk on 14 november"

then sit back and see what works best.

[ineffableone]

There are a lot of different things that can be used for invisible ink.

http://chemistry.about.com/od/chemistry ... leinks.htm

Heat-Activated Invisible Inks
Iron the paper, set it on a radiator, place it in an oven (set lower than 450° F), hold it up to a hot light bulb.

any acidic fruit juice (e.g., lemon, apple, or orange juice)
onion juice
baking soda (sodium bicarbonate)
vinegar
white wine
dilute cola
diluted honey
milk
soapy water
sucrose (table sugar) solution
urine

Inks Developed by Chemical Reactions
These inks are sneakier, because you have to know how to reveal them. Most of them work using pH indicators, so when it doubt, paint or spray a suspected message with a base (like sodium carbonate solution) or an acid (like lemon juice). Some of these inks will reveal their message when heated (e.g., vinegar).

phenolphthalein (pH indicator), developed by ammonia fumes or sodium carbonate (or another base)
thymolphthalein, developed by ammonia fumes or sodium carbonate (or another base)
vinegar or dilute acetic acid, developed by red cabbage water
ammonia, developed by red cabbage water
sodium bicarbonate (baking soda), developed by grape juice
sodium chloride (table salt), developed by silver nitrate
copper sulfate, developed by sodium iodide, sodium carbonate, potassium ferricyanide, or ammonium hydroxide
lead(II) nitrate, developed by sodium iodide
iron sulfate, developed by sodium carbonate, sodium sulfide, or potassium ferricyanide
cobalt chloride, developed by potassium ferricyanide
starch (e.g., corn starch or potato starch), developed by iodine solution
lemon juice, developed by iodine solution

More info with some of the same "inks" and some others not mentioned http://en.wikipedia.org/wiki/Invisible_ink

[robinhoodsghost]

My brothers and I did that when we were kids...good memories.