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On Thursday, October 26, 2000 5:10 PM, Simon L Hartley wrote: > We've (School of RSM) just come into possession of an old admiralty anchor > that's being donated to our new marine studies centre in Coffs Harbour. > The anchor has apparently been placed in fresh water since it's recovery > but no preservation work has been carried out. Can anyone offer any tips > on preserving metal objects or point me in the direction of appropriate > references? Some years back some friends and I recovered an old cannon ball from Sydney Harbour. Although we managed to preserve it - thanks to the eforts of Naval dockyard personnel who knew how to treat it - it inspired me to look at ways of preserving artefacts. I found some good information in a book called, "Underwater Archaelogy: a nascent discipline", issued by UNESCO in 1972. A section by Samuel P Townsend - then of North Carolina State University - describes Standard Conservation Procedures. I won't quote it in it's entirety, but: "Iron and Steel. Ferrous metals are probably the most difficult to treat. Removal of encrustations, corrosion, and chlorides. Mechanical cleaning: clean objects under running water, sing wooden picks, needles, scalpels, chisels and soft brushes. Tougher objects may be brushed with wire brushes and tapped with ruber or plastic hammers. etc. Chemical cleaning: Soak objects in a solution of 10-20 per cent commercil caustic soda or 5 per cent phosphoric acid in water or, after removing calcerous encrustations mechanically, a 50 per cent solution of managanesed phospholene in water heated to 140 - 160 deg F. To avoid damage remove items about every 30 minutes, brush under running water and return to bath as needed. Electochemical reduction:" (Too long to quote verbatim) "Electrolytic reduction: (ditto) Thorough washing under running water: Alternate baths in boiling and cold distilled water: This flushes out chlorides .... from the micropores of the metal. Each bath should last 10 - 20 minutes (longer for larger items), the volume of water being about 20 times the volume of the object. As many as 20 to 40 baths may be required to rinse out all removeable chlorides. Continue baths until the silver nitrate test indiates no chlorides in the used bath water. Give the object a final one-hour bath in either full-strength manganesed phospholene or water made faintly alkaline with caustic soda. Drying: Remove all moisture by heating the object in an oven at 212 deg.F for 8 -48 hours. Extreme heating of largew physically sound objects such as anchors, cannon barrels, projectiles, inplements and tools seems to give better results than lower heats. ........ Protective impregnation or coating: Iron and steel must be completely sealed from air and moisture to prevent freash corrosion. Of the six choices listed below, waxes are probably the most widely used. ...... Impregnation with wax: Submerge the object in molten microcrystalline wax until bubbling ceases. (Parrafin wax, while slightly less resistant to water vapours is also used successfully by many conservators.) Remove and wipe excess wax from object while it is still warm. .... Various commercially prepared clear flat laquers ... are of about equal effectivenes. Apply two or more coats of epoxy resin. ..... sandpaper and then cover with a flat enamel paint. Zinc silicote coating: ...... Manganesed phospholene ..... the object is simply soaked for 1 -2 hours in the full strength chemical and dried at room temperature. Clear plastic embedding .... especially good for artefacts that are too delicate for mechanical cleaning or reduction, or consisting of dis-similar materials....." Simon! The cannonball is obviously a lot smaller than your anchor, but hopefully the same principles will apply. Strike -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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