This very popular liquid hard soldering flux from Grobet provides excellent firecoat protection. Griffith brand pre-mixed Prip's flux from is perfect every time-no need to mess with mixing your own and not getting the formula just right. Griffith brand Prip's flux is a liquid hard soldering flux that prevents the formulation of firecoat and firescale during soldering. Use before primary flux for firescale protection. Contains boric acid. Fluoride-Free.