Bakers no3 soldering fluid bakers 61038 bakers fluid no3 is a liquid flux specially formulated for soldering and tinning of tinned materials copper and brass in many industrial applications the flux is water based containing zinc chloride and other salts which provide an extremely effective fluxing reaction at soldering temperaturesthe flux can be applied by brushing for most applications and is the most convenient method of controlling where the flux is placed alternatively bakers n