Apparatus and method for shielding a portion of an article in an article treatment zone. A plurality of articles are transported in single file through an article treatment zone. The articles may be glass containers, and the treatment material may be a metallorganic decorative spray. In the article treatment zone, mask means closely engage a portion of the article to shield or protect a portion of the article from contact by the treatment material. The mask means may take the form of counterrotating, complementary pairs of shield members which are cammed into engagement with the article at the treatment zone entrance, move in synchronism with the article through the treatment zone and are cammed out of engagement with the article at the exit of the treatment zone.