A KOH preparation is useful when performed on scaling skin lesions, when a fungal etiology is suspected. The scraped scales are placed on a microscope slide, treated with one or two drops of KOH solution, and examined for hyphae, pseudohyphae, or budding yeast. A Tzanck smear is a cytologic technique for the diagnosis of herpes virus infection from vesicles, and diascopy is to assess whether a skin lesion will blanch with pressure.