In 1597,the Jesuit Priest John Gerard was held in the Tower of London on charges of Treason. Gerard had been tortured and was awaiting trial on charges that would certainly have brought him to the scaffold.
Whilst held in the Tower Gerard was able to smuggle secret messages out to friends and I thought it would be interesting to try and re-create these messages.
Apparently, Gerard managed to please the warden by making him a gift of some oranges that he had been sent. Because of this gift, the warder agreed to allow Gerard to send a gift of crosses made from orange peel to his friends in the clink prison (also in London). The warder agreed that Gerard could write them a message in charcoal as long as he was allowed to check the message first.
Gerard wrote a message in charcoal which must have been all that he had to hand with which to write – as you can see from the poor handwriting below, I found it hard to write anything at all!
Once the warder had left the cell, Gerard used the saved orange juice to write another letter onto the paper. Once it had dried,it was used to wrap the crosses and sent to his friends.
All that the recipieint of the message then had to do was to hold the paper up to a fire, as you can see, a new message appears on the paper. I don’t think it is known what Gerard wrote – I would have written something like this asking for help to escape!
Apparently, this was a well known technique for sending messages. Sometimes lemon juice was used, but Orange juice has the advantage of permanently marking the paper once heated up. This quality makes it less easy for a letter to be intercepted and read without detection.
As you can see, from the picture below, the orange juice turns to a dark brown once heated. In practice, it took quite a lot of heat to produce this effect and it was difficult to avoid setting the paper on fire!
I did wonder whether this was where we got the expression “reading between the lines”? – I was unable to find the origin of this and would be interested if anyone knows where this comes from.