Invisible ink is applied to a writing surface with a fountain pen, toothpick or even a finger dipped in the liquid. Once dry, the paper should appear blank or the ink is not an invisible ink. Unless the ink has certain properties that make it visible depending on the surface. For example, there is commercially available red invisible ink. These inks may show up on some surfaces but not all and still be considered invisible ink. The ink is later developed (made visible) by different methods according to the type of invisible ink used. This can be by heat, by viewing under ultraviolet light, or by applying a chemical appropriate for the ink used. Many fluorescent invisble inks that are visible using a black light or UV light simply need to be illumiated with these lights and do not require development.
Invisible inks which depend on a chemical reaction generally depend on an acid-base reaction (like litmus paper) similar to the blueprint process. Developer fluids may be applied using a spray bottle, but some developers are in the form of vapours, e.g. ammonia fumes for developing phenolphthalein ink.
A cover message should be written over the invisible message, since a blank sheet of paper might arouse suspicion. 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.
One can obtain toy invisible ink pens which have two tips - one tip for invisible ink writing, and another tip for developing the ink. Also, invisible ink is sometimes used to print parts of pictures or text in books for children to play with, particularly while they are travelling. A "decoder pen" is included with these books and children may rub this pen over invisible parts of texts or pictures, thus revealing answers to questions printed in regular ink or completing missing parts of pictures. Other ink pens can be obtained commercially that flouresce when illuminated with a UV light. These inks are simply applied and then identified using a black light or other UV light source. These inks are invisible to the naked eye and are only revealed when illuminated.
Some vendors now offer invisible ink for use in computer inkjet printers.  Such inks are usually visible under ultraviolet light. Typical uses include printing information on business forms for use by the form processor, without cluttering up the visible contents of the form. For example, some United States Postal Service mail sorting stations use UV-visible ink to print bar codes on mailed envelopes giving routing information for use by mail handling equipment further down the line before delivery.
Very rarely, invisible ink has been used in art. It is usually developed, though not always. There are artists who use the effect in conjunction with Invisible and other reactive inks and paints to create a variety of effects when used in conjunction with UV lights.