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Conservation

ROSĘJOHNSON

The conservation brief was:

-To advise on suitable storage for the fmds from the time of excavation.

-    The complete treatment of selected finds.

-    The partial treatment of a largcr group of materiał. This generally consisted of identification/analysis and possibly some removai of surface soil or corrosion obscuring details of construction or decoration.

-To advise on outside spccialist analysis.

METALS

Selection and storage

Objects were chosen for fuli or partial conserva-tion by the authors, curatorial and conservation staff. Ali iron was x-radiographed before selection. Limited resources generally mean that only a smali proportion of objects, usually less than 10%, from excavations, are fully conserved. The proportion of conserved objects in the catalogue was greater.

After air-drying objects were individually pack-ed in labelled polyethylene bags. Fragile finds were first packed in transparent polystyrene boxes using acid-free tissue paper for support. This standardised packaging system combines physical protection with high visibility and re-duces physical damage caused by unnecessary handling. The same system was used for treated objects; an inert polyethylene foam (plastazotc) which easily cuts to conform to the shape of the object was also used to support delicate finds.

Selected iron objects were kept in desiccated storage both prior to and after conservation. Excavated iron is often unstable, and furthcr corrosion can occur if the relative humidity (RH) rises above c. 15%. A dessicated cnvironment (RH c.20%) is maintained by packing the iron in plastic freezer-boxes with air-tight lids with a bag of the desiccating agent silica gel. The RH is monitored by an indicating humidity strip placed inside the box so as to be visible through the translucent side. The silica gel is regenerated when necessary.

Examination and analysis

Visual

A stereo binocular microscope with a magnifica-tion rangę up to times 40, illuminated by a raking light, was the standard tool for examination. With this rangę of magnification a detailed study can provide a great deal of information about the condition and technology of an object.

X-radiography

The Conservation Departmenfs Andrex x-ray machinę was routinely used to record the shape and condition of many objects which were obscured by layers of corrosion. In addition, details of basie construction such as rivets, weld lines, solder, and dec.orative elements such as coating, engraving and inlay are visible on the x-ray plates. The presence of a tin coating on iron objects is often, though not always discemible on the plates. Occasionally removal of corrosion from both iron and non-ferrous metals revealed evidence of tin coating and gilding not observed on the plates.

Microchemical tests

The unfamiliar appearance of some of the metals from the waterlogged conditions initially caused some uncertainty about the identity of the metals present. Simple microchemical tests were used to differentiate between coppcr, iron, lead, tin and silver (Ganiaris 1985). Though these tests are by no means wholly reliable, when used in conjunction with microscopic examination they prove a useful preliminary guide.