Before paper was commonplace, the method for keeping your thoughts in order was the wax tablet.
They're surprisingly easy to write on, and are capable of capturing almost the same level of detail as pen and paper. If you make a mistake you can use your finger or the rounded end of your stylus and smooth the wax back to blank again.
There are three designs here,
a pocket 3 leaf version with spots for 4 'pages', (lasercut)
a large single tablet version for a notebook (CNC milled)
*a single page one reminiscent of modern technology. (lasercut)
Here's some more information on wax tablets:
http://en.wikipedia.org/wiki/Wax_tablet
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