I wonder how artists knew which way to twist caps before there were clocks? .And now - something of my dangerous half-knowledge:
![Grin ;D](http://www.intflatfigures.org/BFFS/Smileys/default/grin.gif)
According to Sennelier's advertisment (spelled correctly ?) there were first the clocks
![Wink ;)](http://www.intflatfigures.org/BFFS/Smileys/default/wink.gif)
Paints in tubes were invented only in second half of 19th century.
So - every painter, who owned a clock, had this knowledge when buying his first tube of paint.
Hope this helps.
Joerg