This product is a silver brazing flux.it is intended for use with silver brazing filler metals that melt below 750 degrees. Used correctly it will provide effective fluxing on the common engineering materials- copper and copper alloys (brass),mild steel and stainless steel but not aluminium. 250g tub which is sealed  is suitable for low temperature soldering below 750 degrees. Mix with water into a paste and apply to solder join.