The water is only part of the burial environment
The condition of recovered silver depends on the alloy, surrounding material, salts, oxygen and burial conditions. Freshwater finds can be better preserved than comparable marine finds, but neither label predicts the condition of a particular object.
Marine silver can develop sulfide or chloride corrosion. A dark exterior does not tell you how much sound metal remains, whether the piece can support itself or what information survives in the altered layers.
Sources: Western Australian Museum; Donny L. Hamilton, Texas A&M University.
A corrosion layer may contain information worth saving
The Western Australian Museum emphasizes retaining corrosion products because archaeological information can survive within them. “May” matters: not every crust preserves a perfect strike, and corrosion can already have removed detail.
A household polish or dip is chosen to improve an exposed surface. Archaeological conservation asks a different question: what can be learned and preserved without losing evidence? Do not scrub, polish or chemically strip a newly found coin in order to find out what it is.
Sources: Western Australian Museum; Donny L. Hamilton, Texas A&M University.
A real investigation: the Rooswijk
The Dutch East India Company ship Rooswijk sank on the Goodwin Sands in January 1740. Historic England’s account of the project describes research on recovered coins, including composition and microscopic study of corrosion.
The project also used X-radiography to see objects hidden in concretions. That is a useful contrast with the temptation to remove everything that obscures a surface: the surrounding material can be investigated before it is disturbed.
Sources: Historic England.
Newly recovered wet material needs specialist advice
Do not apply this site’s routine “dry after cleaning” advice to a still-wet archaeological find. Sudden changes after recovery can accelerate deterioration. Wet, mineralized silver needs a conservation plan, including appropriate temporary storage and support.
Keep handling to a minimum, preserve associated material and location information, and promptly contact the relevant heritage authority or a qualified archaeological conservator. Follow local reporting and ownership requirements. Do not mix storage chemicals or try the specialist reduction recipes described in historical conservation manuals.
A professionally conserved object already in a collection is a different case. Keep its treatment and provenance records, and follow the conservator’s storage advice rather than deliberately wetting it again.
Sources: Western Australian Museum; Donny L. Hamilton, Texas A&M University.
Sources & further reading
- Western Australian Museum: Wet Materials: Silver
- Donny L. Hamilton, Texas A&M University: Methods of Conserving Archaeological Material from Underwater Sites
Revision 1, January 1, 1999; Silver Conservation section.
- Historic England: Rooswijk Shipwreck Excavation: The Post-Excavation Phase
Text and explanatory diagrams by Collect Silver. Linked institutions do not endorse this guide.