MadSci Network: Chemistry

Re: What makes disappearing ink disappear?

Date: Thu Jul 13 10:49:53 2000
Posted By: David Sherman, Staff, Sr. Analytical Chemist, Chr. Hansen Ingredient Technology
Area of science: Chemistry
ID: 959087684.Ch

Dear Mr. Miller,

     The basic science behind most invisible ink reactions is related to 
acid/base chemistry and requires pH indicators.  The ink is a colorless 
liquid with either acidic or basic pH.  After the colorless liquid dries 
on the paper is becomes invisible.  However, even though you cannot see 
the ink the acidic or basic properties remain on the paper.  The next step 
in the process is to introduce a pH indicator to elucidate the ink.  The 
indicator changes color when it comes in contact with either the acid or 
base.  Red cabbage juice is normally used as the indicator in classrom 

     The folowing website will take you through the entire process and 
list the volumes required to try the experiment yourself:

     I wish you alot of luck on your book.

Your "Invisible" Mad Scientist Dave (hey where did he go??)

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