Invisible ink

As invisible inks or sympathetic inks ( formerly chemical inks) are referred inks that are either not visible or change their properties after some time.

History

As early as 50 AD Pliny the Elder used invisible ink from the Tithymalus plant. The text was not visible until you heated the parchment over the fire. Especially in the 17th to the 19th century into secret inks were very popular. From this period dates the term " Sympathetic ink " (from the Greek Sympatheia " affection " ), as they were often used for writing love letters. Even Ovid recommends the Romans ' milk to make their correspondence for Blank Called invisible; one must then sprinkle only carbon powder on it. 1653 suggested the Frenchman Pierre Borel to write with a lead acetate solution and to make the lettering visible with liver of sulfur solution. Jacob Weitz, personal physician in Gotha, discovered the property of cobalt chloride to produce writings that are almost invisible after drying, on the other hand when heated out clearly in blue color and disappear again when it cools.

Later inks have been developed that can be made visible with acid or by UV light, or disappear after some time. Even today, the secret inks are not yet gone out of fashion, as children, they like to use "secret " messages.

Examples of simple inks

• Juice of lemons or onions kitchen ( visible when heated )
• Vinegar ( becomes visible when heated )
• Milk ( can be seen on heating )
• Ink eraser ( can be seen on heating )
• Phenolphthalein ( is visible when painting with ammonia solution and disappears later ); Variant: phenolphthalein mixed with a little ammonia solution (font disappears after a short time )
• Tannic acid ( becomes visible when painting with iron (II ) sulphate solution )
• Solution of sodium carbonate (soda ) (will be visible when brushing with a 1% phenolphthalein disappears and later )
• Cobalt (II ) chloride solution ( is visible on heating and disappears later )
• Potassium thiocyanate solution ( is by spraying with iron (III ) chloride solution visible)
• Fruit juice invisible ink (to be visualized by UV light or heating )