Fig. 8

Igniting wood and leafs: chemical diversity of plant ash as network modifier. Analyses: Ref. see under Fig. 1. a Ternary diagram with chemical and physical/thermal data of medieval K–Ca glass represented as points (right area) and wood ash to the left (B beech, L beech leafs, W wood in general; F fern, R rice, S wheat straw). The composition of beech ash (trunk) is dominated by a varying lime content. Fern and cereal ash contains less lime, cereal ash much silica. b Same diagram with selected beech wood ash from calcareous habitat (CH-Jura, upper B) and silicate habitat (D-Black Forest, lower B), both connected by a red tie-line with the projection point of network former quartz (right corner). Calculated intermediate mixing proportions of ash and quartz are indicated with b. The four boxes represent calculated glass compositions, based upon Theophilus’ recipe “two parts ash + one part sand” assuming fresh ash (left two boxes) and stores ash (right two boxes). c The silica content of ashes from trunk and leafs of different plant species (17 pairs, data from Wolff (1871). d The lime content of trunk vs leafs from the same species. e Mixtures of selected plant ashes and quartz, connected with tie-lines. According to ash composition and mixing proportions of ash and quartz different melting temperatures result (calculated compositions): high-lime/native beech ash (≈1400 °C), low lime beech ash or beech ash extract (≈1200 °C), ash of native fern (≈900 °C), ash of native wheat straw (≈800 °C). Ash of native wood and ash extract differ by their respective CaO- and P₂O₅-contents (not shown in this diagram). f Individual parts of one and the same plant, e.g. winter wheat (triticum aestivum), contain nearly the same lime, but a strongly differing silica and K₂O-conent. By blending ignited chaff and stalks of one and the same plant, melting temperatures varying from ≈800 to 1700 °C are possible