The photo below shows me applying liquid flux from the jar cap onto the liquid flux which is always applied prior to soldering. When using flux, its best to pour a small quantity into the cap and use that, rather than dip the brush into the jar. The same holds true for the patina. At this time in the process, I tack-solder each panel. I use 60/40 tin/lead solder which melts at 370 degrees. Safety first, I always wear a protective breathing mask when soldering. Look for a mask which is specifically suited to abate lead and flux fumes. (One of mine can be seen in one of the photos below).
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