Amine complex of hydro-polycarboxylic acid in aqueous solution. pH: approx 4.0
Treatment selectively ruptures the bond between the base metal and corrosion layer, reducing rust to a sludge which is easily wiped or brushed away. Clean water rinse stops the process.
Even relatively prolonged immersion over several days has no significant effect on sturdy metal, thus giving the conservator complete control over the process – however, frequent checks should be made until the metal has returned to the required condition.
The benign nature of the product eliminates work and health hazards associated with common de-rusting systems such as those based on phosphoric and hydrochloric acids. Normal ventilation and common-sense hygiene procedures should be observed, with gloves and protective clothing advisable.
Following treatment, metal surfaces are stabilised for up to 14 days, giving ample time for applying long-term protection (such as Renaissance micro-crystalline wax polish, which confers a tough – but reversible – glass-clear lustrous finish).
Bi-metallic electrolytic effects between dissimilar metals are insignificant in treatment periods of up to 48 hours. There is no attack on zinc coatings, except significantly prolonged immersion.
Treatment is most effective at temperatures between 10ºC and 20ºC. Colder solutions slow the action still further – a useful quality when objects are left immersed over a weekend. Contrast this safe, gentle handling of metals with the more vigorous, often deleterious action of mineral acids.
Loose rust or scale should be wire-brushed and surfaces de-greased to allow optimum performance. Immersed objects will be clear of light corrosion in as little as two minutes. During longer immersion for heavier rusting, periodic checks can be made by rubbing the object with a finger. Brushing speeds up the process.
Storage and treatment vessels of mild steel, porcelain, rubber, polythene or other plastics are suitable. Galvanised, tin, zinc or lead-lined tanks are NOT suitable.
After use of the solution, separate it from any sediment by siphoning it into a clean container and top up occasionally with fresh solution. The product remains effective for many weeks.
It can be effectively used on iron, bronze, copper and copper alloys, brass, steel, zinc and galvanized materials. It also effectively cleans SCALE and rusty water stains.
Varnish films on metal surfaces might well absorb the liquid in prolonged soaking, causing it to soften and be easier to strip off.
De-corridor is not sufficiently active enough to attack sound metal, although colour change could occur after prolonged soaking e.g. 12 hours or more.