One technique that might help.
Sheet moves as it expands, so if you heat your strip unequally,
especially with a small flame you will have difficulty keeping the
two ends still, and flat and together.
You need a large propane flame.
Firstly I take a suitable flat fire brick sheet.
Get your silver ready with the ends fluxed.
Pre-heat the brick sheet, get the central area really hot where the
silver joint will lie.
Place the the silver ends together on the pre heated area and heat a
large area on each side of the joint gradually concentrating the heat
on the join.
Put a small piece of solder on each side of the join line and when
they both melt, stick solder the rest of the joint.
Twist two or three solder wires together if necessary. well fluxed.
How thick is your silver, as silver less than 1 mm may be just to
thin to join as there is bound to be some discrepancy between the
I made several large mirror and picture frames and successfully
joined the corners this way.