A couple data points for you:
An acquaintance refurbishes Stanley miter boxes, does a good job, and
his recipe is the same as the one described.
I bought a gallon, I think, of Pontypool Asphaultum back in 2001. I
used it back then to coat a couple of Veritas vises that were green. It
worked out quite well. Back then I repackaged the product into pint
cans and offered them to the list but had no takers. A few months ago I
opened one of the pint cans, noted it appeared to have stored quite well
and used it again to coat some green Veritas vises. I baked the vise
parts, sort of, by sandwiching the parts between a couple 100 watt
bulbs. I baked the parts for about a day. They were dry to the touch
but they did not pass the fingernail test for hardness as suggested in
your article. The parts were satisfactory dry and the installed vises
parts don't get any handling in use so I was satisfied.
About that same time I was discussing old pianos with a restorer and the
subject of japanning came up. I explained my experience to date with
the Pontypool Asphaultum and agreed to perform an experiment to more
properly apply the material. I located a cast iron part from a previous
piano effort. The piece is only about 1x3x1/2 so easy to handle. I
clamped it with vise grips on a pivot nipple on the part. The product I
have is very thin. I had to apply three coats. For each coat I kept
the part under a 100 watt bulb and turned it every ten minutes or so for
about an hour to eliminate any runs or sags. It had set up pretty well
after an hour. After the third coat had dried over night I put the part
in a toaster oven, used an oven thermometer to set 450 degrees and left
it there for two hours. After the baking I found the part to be
perfectly shiny and hard enough that it cannot be scratched.
The information above doesn't really do you much good because I'm pretty
sure the current recipe for Pontypool Asphaultum is not the same as the
2001 recipe. They insist their recipe today does not need to be baked
so it is certainly different.
I have enough of the Pontypool to last several lifetimes. I'm not a
restorer. I bought it to paint the vises I bought. I never expected to
have a similar project 15 years later. If I needed to do it again, I'd
go with the recipe you have. I had discussed this same recipe with the
fellow that refurbishes the miter boxes. He offered, "About the
japanning, the recipe you have is a good start. what I do after that is
add more asphaltum until it is very thick, thicker than maple syrup. It
can take up to a day before it's at it's final consistency. You can add
some powder to it and it seems fine and come back the next day and it's
like past wax, if so just add more turpentine. The stuff is very
resilient, I add all three ingredients at different rates and it never
fails to work. Also, it seems to last forever, never had it go bad on
me, actually, I don't see how it could.... , the stuff I make needs to
be baked on at 400 degrees, so It's fully cured in 2 hours "
Hope this helps...
In Beautiful downtown Nottingham, PA