invisible ink

[mathew]

Hey guys.

I am making this prop from a book, but I need a heat activated invisible ink that turns black ( really black not grey).
I have no idea what i could use, does anybody has an idea to help me?

 

[Brigandia36]

lemon juice ?

 

[mathew]

lemon juice ?

too brown, thank's for the suggestion

 

[Guppzor]

The few heat activated ones that I know of indicate brown (lemon juice, milk, etc), so I would be interested in finding a black one as well.

 

[whitehammer]

I think you would be very lucky to find an ink that will change from invisible (clear) to opaque black without using some very nasty or expensive chemicals, (spec if it had to be heat activated)
Ive only ever heard of ones that turn to brown. Maybe if you looked at paper (type of litmus?) It'd probably work if you used thermal paper like in till receipts with something to block rest of paper turning black, depends how bad you want it.

 

[mathew]

well the problem is that I am not looking into this for a prop alone.
I have a prototype which needs heat activated invisible ink that turns black and heat activated invisible ink that turns red. so Receipt paper will work for the prop but not for my prototype, therefore I need ink.
so if anybody has an idea...

 

[Conqueror_Worm]

About a year ago the CIA declassified a bunch of secret ink recipes from WWII. The documents are available at this site. They are near the bottom of the page under the heading "CIA Declassifies Oldest Documents in U.S. Government Collection"

 

[mathew]

About a year ago the CIA declassified a bunch of secret ink recipes from WWII. The documents are available at this site. They are near the bottom of the page under the heading "CIA Declassifies Oldest Documents in U.S. Government Collection"

It says the site can't be displayed now.
but thanks

 

[Guppzor]

It says the site can't be displayed now.
but thanks

It appears to be up from this end. Just about to check the docs out and see if there is interesting inside.

 

[whitehammer]

they are OK at my end & Im not in the U.S.

 

[Conqueror_Worm]

Try these links-
Secret-writing-document-one.pdf
Secret-writing-document-two.pdf
Secret-writing-document-three.pdf
Secret-writing-document-four.pdf
Secret-writing-document-five.pdf