Les cendres v\'eg\'etales, mati\`eres premi\`eres des verres et des \'emaux : un exemple, les cendres de v\'eg\'etaux utilis\'ees par Fr. D de Montmolin

TL;DR

This paper analyzes the composition of various vegetable ashes used historically as modifiers in glass, enamel, and ceramic production, highlighting their high alkali content and compositional variability.

Contribution

It provides a detailed compositional analysis of diverse plant ashes, challenging the assumption that variability is solely due to recycling.

Findings

Vegetable ashes have high alkali and silica content.

Significant compositional variation exists among ashes from different sources.

Recycling is not the only factor influencing ash composition.

Abstract

The powdery nature and high alkali content of vegetable ashes make them ideal raw materials to be used as modifiers of silicate compositions (glasses, enamels and ceramics). Their utilisation since ancient times is described in the literature of the history of glasses, but studies on the analyses of their composition are still limited. We discuss here the compositions of tree and shrub ashes (wattle, hawthorn, oak, green oak, olive wood, elm, poplar, apple tree, vine shoot), of plants (carex, fern, dogwood), of cereals (wheat, maize, rice), threshing waste and hay, mainly harvested in Maconnais, near Taiz\'e (Sa\^one-et-Loire, France), by the potter Brother D. de Montmolin. The contributions in alkali modifiers (Na2O, K2O), alkaline-earth (CaO, MgO) and in silica are discussed in view of the data gathered from the literature of the history of techniques used in the production of ceramics, enamels and glasses. The huge variation in composition is usually attributed to recycling and is questioned by the very broad range of compositions that we obtained in the analyses of the ashes.