Inspired by my childhood interest in mysteries, the spy pen series are a set of colored felt tipped pens, each with a different invisible ink solution (ranging from lemon juice, to baking powder & water, etc.). The pens will include instructions on them on how to make more invisible ink, and will be refillable via screwable rear cap. The messages written by these pens can be read by holding them up to a small heat source like a light bulb or radiator.

The pens will allow for hours of both individual and group enjoyment amongst youngsters as they experiment with making the invisible ink solutions and write messages to their friends. The pens will be made out of durable, high impact plastic which will be safe for the children to use. However, due to the need for heat to read the messages, parental supervision is strongly recommended and this toy should be used by children over the age of 10.

• Construction Cost: < $2 per pen
• Age: 10+ (Adult Supervision Recommended)