We investigated the long-term light variations of six young irregular variables, all of them UX Orionis stars or related objects. For this aim we determined new photographic magnitudes for the five stars VX Cas, BH Cep, BO Cep, SV Cep, and RZ Psc and made use of similar data for WW Vul published independently. The magnitudes were derived from Argelander brightness estimates performed on plates of the Harvard College Observatory and Sonneberg Observatory plate collections. The data cover a

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... of about 100 years and are available at the Centre des Données Stellaires, Strasbourg. The new data were supplemented by multicolour photoelectric measurements taken from the literature and visual estimates collected by the AAVSO. The resulting lightcurves are displayed and discussed. Algol-like minima are observed with all the stars. Their properties are discussed under the presumption that they are caused by circumstellar dust clouds orbiting the stars. Parameters of the circumstellar dust shells are derived from modelling the observed infrared excess radiation and compared with constraints from the light variations.