A ceramic body designed for brilliance The bright art of 16th-century İznik tiles begins with a specialized ceramic body, a composite material known as fritware or stonepaste.%%CITE_1%%%%CITE_2%% Unlike traditional clay earthenware, İznik fritware has a high quartz (silicon dioxide) content, typically 65% to 75%.%%CITE_3%%%%CITE_4%% This quartz sand was mixed with small amounts of fine white clay and a glassy substance called frit.%%CITE_1%%%%CITE_5%% The frit, made from powdered quartz heated with soda and lead oxide, acted as a binder for the quartz particles during firing.%%CITE_1%%%%CITE_3%%
This quartz-rich composition was a deliberate technological choice. The Ottoman court potters were trying to imitate the prized white-bodied porcelain arriving from Ming Dynasty China. While chemically different, the fritware body provided an exceptionally hard and brilliantly white canvas that did not warp or discolor at firing temperatures around 900°C. Before the pigments were applied, the ceramic body was coated in a white slip of similar composition, ensuring a perfectly smooth, white surface for the decoration. The near-identical thermal expansion coefficients of the body and slip were critical to prevent cracking during firing.
A global palette of metal oxides
The deep, lasting colors of İznik tiles come from a carefully controlled application of metal oxides painted under a transparent glaze. The base glaze itself was a lead-alkaline-tin composition, containing 25-30% lead oxide, which acted as a flux to lower the melting point. Modern analysis using non-destructive X-ray fluorescence (XRF) shows the global origins of these materials.