Iron is one of the most difficult metals to clean and conserve. To do this properly, you have to go through a (lengthy) process in a number of steps. First remove the (coarse) rust and then desalinate. Desalting is very important because otherwise an object can start to rust again due to the remaining chloride salts. These should be removed before preservation. Then stabilise it with tannin and finally conserve it with paraloid B72 and/or microcrystalline wax.
Iron from an archaeological context has been in contact with salts, of which the chloride salts are the most harmful. These have been partially absorbed into the object. They accelerate the degradation process once the object has been excavated. To slow down the decay as much as possible, the objects have to be desalinated. The desalting is done in a sodium-sulphite solution. This traps loose chlorine ions. Make a solution of 6 % sodium sulphite and 3 % caustic soda in demineralised water. Add 9 dl of demineralised water to the contents of the jar or, in the case of a small object, 50% of the recipe or 25% of the recipe.
Put the object in a container, preferably airtight. The duration depends on the thickness and porosity of the object and the temperature. On average, at 20 degrees 2 weeks, at 50 degrees 2 days. A cannonball can take up to half a year. A large cannonball up to a year. With larger objects such as a cannonball, replace the desalination solution regularly. In the beginning every month and later every few months. To find out if the object is ready, use a conductivity meter to check whether there are any chlorides left in it. First put the object in demineralised water.
When this process is complete, neutralise it in demineralised water for a few days and then soak it in a tannin bath or smear it with a tannin solution and leave it there for a day. Then dry quickly in an oven at 120 degrees and preserve with paraloid B72 or Microcrystalline wax.
Storage: Store in a cool, dry place and out of reach of children.
Always work safely when cleaning and conserving soil finds. Wear protective gloves / protective clothing / eye protection / face protection.
Sodium hydroxide can cause severe burns.
IF IN EYES: Rinse cautiously with water for several minutes; remove contact lenses, if possible; continue rinsing.
IF SWALLOWED, seek immediate advice from an anti-poison centre or doctor.
Note: This product is only shipped within the E.U.
Download here the safety sheet:
Iron is one of the most difficult metals to clean and conserve. To do this properly, you need to go ..
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