I thought the trick was to write notes to your pals using lemon juice as ink then they could read it if they warmed the paper up. A bit hazardous if using an open fire for a heat source. Maybe that was why there were sand buckets. 
PS can't remember any sand buckets at school.
PS can't remember any sand buckets at school.
Gardening is an excuse not to do housework
Greetings from Salisbury
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