Glass and enamel

Study of vitreous materials focuses on the chemical nature and alteration state of the glass.

From surface replicas or micro-samples, many clues as to the antiquity or modernity of the material can be identified. 

surface replicas

Surface replicas enable non-invasive analysis of the object. A thin sheet of cellulose acetate, previously soaked in acetone is applied to the area of interest. Once dry, the sheet is removed, fixing the deposits and microparticles of the alteration layers. The surface state and tool traces are also studied on the surface of the replicas.

Replica on the surface of a blue glass plate from the Abbassid period, moulding the surface of the engraved decoration.

The composition of glass and enamel

The chemical composition of a glass and the nature of the chromophore elements in an enamel are often indicative of a particular period or civilization.

• The use of lead arsenate as an opacifier, for instance, is documented from the 19th century onwards in Europe. Older glasses generally contain tin oxide.
• Chromium-based pigments are typical of « modern » glass.

Using the PIXE (Particle Induced X-Ray Emission) or a LA-ICP-MS (Laser Ablation Inductively Coupled Plasma Mass Spectrometry) method, the trace element composition can be used to determine the provenance and origin of a glass.

Alteration of glass

Numerous degradation factors, such as variations in temperature and humidity, cause physical and chemical changes to glass.
Leaching of alkaline elements, surface iridescence and the formation of characteristic facies (microbubbles), are some of the signs of age observed on the surface of archaeological glasses.

Area of iridescence on the surface of an Abbassid flat in relation to the formation of a multilayered, bubbly weathering material.