It really will depend on the trype of result you want. If you use a wash with thinners or turpenoids in it, it may affect the Alclad. I did my Honda F1 engine with Alclad white aluminium and then a thinned enamel wash in order to get a dull oily look. Watercolours and inks will have no affect on the Alclad, neither does Tamiya Acrylics mixed with Windex or a soapy solution.