| 摘要 |
<p>The process uses a.c. and a bath of the 'barrier layer' type contg. tin sulphate, esp. stannous sulphate; a mixt. of lactic- and salicylic- acids; H2SO4 added to keep the pH near to 1; metacresol-sulphuric acid and an equal amt. of pure metacresol; and an antioxidant. Continuous filtration of the bath is used with decantation for partial removal of sediment. The antioxidant is pref. a biphenol; hydroquinone; a pyrocatechol; or formaldehyde; and filtration pref. treats 50% of the bath vol. each hour. The a.c. is pref. at 17 volts; and the counter-electrode is pref. made of a non-oxidisable metal. The bath acts rapidly to obtain dark bronze or black colours which have improved stability to light or corrosion as compared with conventional colouring baths.</p> |
