A diary page seemed blank until exposed to heat, revealing a confession. How was this message concealed?

Category: Mystery · Difficulty: expert

Hint: Think about materials reacting to physical changes

Answer

The ink was made from heat-sensitive substance

Explanation

Special ink that becomes visible only when heated was used to hide the confession.

This is a expert mystery riddle — one of the harder riddles here. The answer is The ink was made from heat-sensitive substance.

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