The Flash‐age Fixation of Vat Prints Using Sodium Sulphoxylate Formaldehyde as Reducing Agent

Since it was introduced, the flash-ageing process has been modified by the introduction of acetaldehyde sulphoxylate as the reducing agent, to overcome the difficulties of handling and of plant design associated with the low stability of sodium hydrosulphite. The universally used reducing agent for vat printing is sodium sulphoxylate formaldehyde, but this is insufficiently reactive for use in the flash-ageing process as originally operated. It has now been shown that, by the incorporation of a suitable reduction catalyst into the print paste, sodium sulphoxylate formaldehyde can be sufficiently activated to render it suitable for use in flash ageing. This paper reviews the steps in the investigation leading to the use of such a catalyst. If the sodium sulphoxylate formaldehyde is incorporated in the vat print paste and the catalyst in a caustic alkaline padding liquor, vat-dye discharge styles can be produced by flash ageing. This process can be extended to the fixation of a reactive dye background in the same flash-ageing process as the fixation of the vat illuminating pigments.