Jeanne Werge-Hartley's excellent reference "Enamelling on Precious
Metals" provides a recipe for "FM Solution", a similar solution, in
my understanding, to that of Prips flux.
I trust that I am not infringing her copyright and would recommend
any enamelling "orchidist" who does'nt already possess the volume to
sprint off to your nearest good bookstore and seize a copy.
The FM solution has worked for me exactly as specified in her
reference, most particularly in its ability to "rinse clean" in water
leaving no borax glass residues and completely eliminating any
appearance of firescale on sterling pieces with cross sections up to
5mm thick and 270mm wide. These have usually been fired at the 830-
850 celcius range.
Her book states " It is essential to be accurate in measuring these
ingredients", an instruction I followed to the letter.
Boric acid 53.2g
Sodium acid phosphate 35.0g
Sodium hydroxide 3.4g
Borax (powder) 35.0g
Distilled water 0.75 ltr
Teepol - 14.2 ml (teepol is an English liquid dishwashing detergent,
I substituted with an equivalent new Zealand product without any
" Mix all the chemicals together with the teepol and distilled water
in a litre container and shake gently until dissolved. The distilled
water can be added lukewarm to assist the mix".
"The metal must not be highly polished; the surface should be
slightly matted with fine garriflex or fine emery paper. Paint or
spray the surface with the solution and allow to dry for maximum
effect. The solution should always be clean so, to ensure this, it is
best to work with small amounts and replace it frequently".
While my use of it has been primarily aimed at preventing firestain
during the kiln firing of the enamels I have found it to be equally
effective in firestain prevention during torch soldering operations.
In my experience it does function as a flux and will encourage solder
flow, sometimes into unwanted locations, to prevent this I simply
wait until its dry and circumscribe the solder area/seam with a soft
lead pencil to inhibit.