Lonelygirl15

A cover message should be written over the invisible message, since a blank sheet of paper might arouse suspicion that an invisible message is present. This is best done with a ballpoint pen, since fountain pen writing may 'run' when it crosses a line of invisible ink, thus giving a clue that invisible ink is present. Similarly, invisible ink should not be used on ruled paper, since it may alter or streak the colour of the lines.

kellylen wrote:instead of dipping it in lemon juice, which may ruin the card completely if its that wet from the juice, i suggest taking a paintbrush and brushing the lemon juice on.

Luv2Luvem wrote:

kellylen wrote:instead of dipping it in lemon juice, which may ruin the card completely if its that wet from the juice, i suggest taking a paintbrush and brushing the lemon juice on.

I really want to make sure this works. I think dipping would be better.

acidfingers wrote:Yeah, accuracy is the key here. If we only get it partially exposed to the lemon juice, it may not fully show the invisible ink, and could destroy the card in the process. It's got to be a surefire way like dipping the card or possibly pouring the lemon juice on the card in a tupperware container

Interception of secret messages

Any invisible ink can be made visible by someone who is sufficiently determined, but the limitation is generally time available and the fact that one cannot apply hours of effort to every single piece of paper. Successful use of invisible ink depends on not arousing suspicion.

Telltale signs of invisible ink, such as pen scratches from a sharp pen, roughness or changed reflectivity of the paper (either more dull or more shiny, usually from using undiluted ink) can be obvious to a careful observer who simply makes use of strong light, a magnifying glass and their nose. Also, key words in the visible letter, such as 'red cabbage' or 'heat', in an odd context may alert a censor to the use of invisible ink. Invisible ink should not be used with glossy or very smooth paper types, since the sizing of these papers prevents ink from being absorbed deep into the paper and it is easily visible, especially when the paper is examined under glancing light. There are, however, commercially available inks for non-porous surfaces that are only visible under ultraviolet light and are otherwise virtually invisible on these kinds of surfaces.

Using either ultraviolet light or an iodine fume cupboard, messages can be quickly screened for invisible ink and also read without first permanently developing the invisible ink. Thus, if a censor uses this method to intercept messages, he may then let the letter be sent to the intended recipient who will be unaware that the secret message has already been intercepted by a third party.

A "screening station" could theoretically involve visual and olfactory inspection, an examination under ultraviolet light and then the heating of all objects in an oven before finally trying exposure to iodine fumes. In theory, some invisible inks may even show up using a camera sensitive to infrared light.