First try went surprisingly well, but not perfectly, so of
course I spent a day or two dialing everything in for future
reference. The directions on the package leave out a few helpful
tips.
Paper setting
Most importantly, the instructions stress over and over that a
laser printer can melt the decal medium*, and so recommend settings
that... did not work well in my particular printer.
I have a Color LaserJet MFP277dw, a popular choice for home
printers right now (and I'm pretty happy with it). This printer
has a low-temp fuser, and the recommended 'plain paper' setting
for decals wasn't fusing the toner to the decal sheet reliably. The print tracked
down the page (left side of the pic), and also tended to rub off
after printing. The slower, higher-temperature 'transparency'
setting works perfectly (right side of pic), and the print is
durable to rubbing and scraping. Win.
Soaking and sliding
Secondly the instructions recommend soaking in hot water (good
idea) for 20-30 seconds (in boiling hot water, maybe). I found
a minute to be more like it, it depends on the actual
temperature. Ideally, pull the decal out just before the edges
start lifting from the backing.
The decal itself appears to be a vinyl of some sort. When
it's hot, it's stretchy and pliable. When it cools back down, it
becomes fairly stiff. In the usual 'building models' case, you
probably want the label to conform to the target surface, so
slide and apply while hot (being careful not to stretch the decal
entirely out of shape).
For my use (meter scales) I want the decal to preserve its
dimensions exactly. Letting the decal cool to room temperature
before application works perfectly!
*The decal media is Papilio Laser Water-slide Decal Paper
from texascraft.com. I've been using various specialty Papilio
inkjet and laser media for more than ten years and have always
been happy with them. These days it needs to be said: I've not
been paid for any kind of endorsement, and have not been gifted
any free or discounted product. I'm just a happy customer.
There may be better stuff out there, but I've not bothered to
look for it--- and that's coming from a perfectionist who's
never satisfied with anything.