potassium tetraborate is also found in brazing fluxes it readily dissolves metallic not refractory oxides at high temperature almost as well as potassium pentaborate also another replacement option at a fraction of the cost it was selected as an option to consider in the replacement of boric acid anhydrous potassium tetraborate alone does not melt until 1500 u00b0 f 816 u00b0 c and is hygroscopic converting to the tetrahydrate with prolonged exposure to humidity hydration of powdered anhydrous potassium tetraborate fluxes causes an uncontrolled change in flux properties over time and imposes unnecessary conditions and or processing during manufacture hydration is an exothermic process that causes manufacturing concerns while anhydrous powdered potassium tetraborate flux does perform adequately the flux does not melt until the faying surface is hot enough to form additional oxides which will subsequently need to be removed additionally this flux will not u201c hot rod u201d well due to the high melting temperature for all of these reasons potassium tetraborate tetrahydrate was chosen as a preferred replacement over anhydrous potassium tetraborate as a boric acid substitute the invention will now be described by a series of non limiting examples in one embodiment of the invention a black high temperature paste flux is described the composition of which includes a mixture of water potassium tetraborate tetrahydrate potassium bifluoride boron udylite udylite 62 is a product of enthone u00ae 350 frontage road west haven conn and fumed silica in the following weight percentages in another embodiment of the invention a low temperature boric acid free paste flux will include a mixture of water potassium bifluoride potassium tetraborate tetrahydrate potassium fluoroborate pigment udylite and fumed silica in the following weight percentages copper phthalocyanine green no 7 was employed in several compositions as.