Abstract: A method, and aqueous emulsion, for coating a metal part with a peelable mask that is resistant to attack by the strong acid and strong base etchants used in chemical milling are disclosed. The method comprises contacting a polyvalent metal cation salt-surfaced part with an anionic emulsion for a time period effective to coat the part. The anionic emulsion includes coalescent rubbery particles and pigment and has a total solids content of at least about 10 weight percent. The weight ratio of pigment to rubbery particles is about 0.1:1 to about 2:1, respectively.

Abstract: A method of coating a metal part with a peelable mask which is resistant to attack by the strong acid and strong base etchants used in chemical milling is disclosed in which the metal part is surfaced with a layer of polyvalent metal salt, such as calcium nitrate, and then immersed in a high solids content anionic emulsion of coalescent rubbery particles heavily pigmented to contain at least about 45% total solids content and at least 20% pigment, the pigment to binder ratio being from 0.75:1 to 1:0.51. The salt-surfaced metal part is held in the anionic emulsion until the desired coating thickness has been anodically deposited thereon, and then the coated part is removed and baked to complete the formation of the mask. The rubbery particles are preferably constituted by an anionic polychloroprene homopolymer emulsion which is used in admixture with a curing agent for the homopolymer, like zinc oxide, and a polyvinylidene chloride latex.