Planning for the second and final season at St Leonard's is proceeding apace. A variety of courses of 1 to 10 days duration are available throughout the excavation, and are open to anyone over the age of 16. No experience is necessary, just enthusiasm to have a go - so why not book now! WARNING - the modules in July are filling up fast.

This month's update looks at the work of YAT's Conservation Department. For almost 30 years the York Conservation Laboratories have worked constantly to study and preserve the huge collections of finds of all types from the many excavations undertaken by YAT. The carefully conserved, packaged and stored collections, backed up with computerised records and images, makes YAT's archive one of the best urban research collections in the country. Specialising in the conservation of freshly excavated finds, the five-strong Conservation team offers their services further afield, particularly in the areas of metals conservation, and the recording and stabilisation of waterlogged organic materials. Structural timbers and boat parts up to 4 metres long can be handled in the specially designed facilities in the York Archaeological Wood Centre, where work is undertaken under contract from institutions from around the country and overseas. Students studying conservation at British and overseas institutions are able to gain valuable experience through work placements at the Laboratories.

The Conservation Labs of York Archaeological Trust are well equipped to deal with the conservation needs of a wide range of archaeological materials.

Finds from YAT's excavations are all conserved in YAT's Conservation Laboratories. One of the best finds from the 2001 season at St Leonard's was that of a fragment of medieval glass.

Fragment of medieval stained glass. The glass seems to show the wing of an angel who is swinging a censer, and the head of another angel with its halo.

Medieval window glass is often found decorated with painted designs and representations, and is of a type known as 'potash glass'. It is a fairly unusual archaeological find in York and normally relates to the destruction or alteration of some ecclesiastical building. Once buried, potash glass will normally be attacked by chemicals in the soil water, which will turn it almost black in colour and make it very fragile. If allowed to dry without conservation treatment, corroded glass will rapidly disintegrate. The conservation process will often involve chemically cleaning the corrosion crust from the surface of the glass, followed by consolidation with a water-based synthetic resin solution. The glass can then be allowed to dry slowly but is still rather fragile, requiring special protective packaging.

Student Daphne Tourres applying a consolidant to some of the window glass fragments from the St. Leonard's site.