Aluminium in Finn chambers reacts with cobalt and nickel salts in patch test materials.

Aluminium has a greater affinity for electrons than cobalt and nickel. Therefore, cobalt and nickel ions would be expected to exchange with metallic aluminium in Finn chambers. This theory has been proven to be valid, as shown in 2 series of experiments: first, cobalt and nickel salt solutions (0.25 M) etch a metallic aluminium surface; secondly, aluminium Finn chambers kept in 10(-3) M nickel salt solutions significantly reduce the concentration of dissolved nickel. Dichromate solutions do not etch an aluminium metal surface significantly. Petrolatum, which is routinely used as vehicle in standard patch tests, probably protects the aluminium of Finn chambers from the interaction of cobalt and nickel salts. The interaction may have significance in tests with solutions.