Volcanic glass, used in its powdered form as pounce on parchment; in its consolidated form, it was employed to scrape parchment for reuse as a palimpsest.

Michelle Brown
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    Pierre ponce

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    Pietra pomice

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    Piedra pómez

Michelle Brown, Understanding Illuminated Manuscripts (Malibu, CA: J. Paul Getty Museum in association with the British Library, c1994).

Ronald Reed, The Nature and Making of Parchment (Leeds: Elmete, 1975), 87-89.