Part 1 a couple of weeks back , using low temperature set soldering iron.

Have tried chemically using both potassium chromate and potassium iodide but
cannot make either work with elemental/eutectic lead. Not having a source of
conc nitric acid and colour of tin iodide being orange and tin chromate
being brown, so not that different to the yellow lead salts, may not have
worked anyway. I gave up along those lines after trying boiling up with
acetic acid and separately washing soda failed.

2 more physical tests.
Grey mark on paper.
Scrape back surface of the solder and rub a specific number of times with
some copier paper over a cocktail stick. Leaded solder leaves a much darker
grey mark, nearer black, on the paper.

Indentation test shows promise.
The following using a well worn automatic centre punch, so a new sharper one
for use only on soft metals is probably called for. This one, existing
spring replaced with a lighter one giving a load before trigger of 3.5Kg.
Comparing block of copper,Al, roofing lead and off the roll solder
wire,63/37 and 85.5/4/.5 silver solder laid over the lead as a soft anvil.
Steel rule with 1/100 inch markings and a x30 basic microscope
Measuring diameters of the indentations (x10 thou/mil)
Cu 1.5
Al 2.5
high tin solder 3
SnPb 4
Pb 5


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://diverse.4mg.com/index.htm