Oxyfuel.
I find the world is changing faster than my shop... the materials I'm most comfortable using are getting hard or impossible to get... I had gotten used to "raw" bronze rods that you (powder)flux yourself, but there are some benefits to the flux pre-coated rods (all anybody stocks 'round here) as well... for cooler alloy (silver-solder) I paste flux the parts... in every case the primary issue is cleanliness. I clean before any fitting, cutting, grinding or sanding, and again before fluxing or heating. If your bronze filler is old and/or poorly stored you may have to clean oxide and oils from that also. Your cleaning materials must be clean themselves; you can drag in contamination from sponges rags sandpaper and abrasives which can confound you.

It may be best to consult the filler manufacturer for advice on fluxes for their alloy.

Some time ago, less than a year, there was a link to flux information from I think an outfit in Canada posted around here somewhere.

Good luck
d

Yes, most paste fluxes for silver alloy brazing are thinnable with water. Just thin it until it will spread onto the work easily. I did some brazed lap joints in 24 guage stainless and thinning the flux made the braze flow much easier and with less oxides forming. Don't be skimpy with the flux, cover the area of the joint and well beyond it, this will help keep the oxides from forming on the heated area. With stuff like stainless you'll get oxides that are unbelieveably tough to remove if it's not fluxed enough. They make acids to clean them off, but I would rather not even have them in my home shop, due to the concentration. Also, make sure you ventilate well with the fluxes. Many of the white paste fluxes contain Potassium bifouride. These release hydroflouric acid when used. The vapors from this stuff are big time nasty.