trouble with enamelling solder

[NickD]

I've been trying to solder a pierced sheet,which I first sweat soldered, to a backing.
It starts fine. The solder began to melt, I put it in pickle and then brightened it with a file.
However, on putting it on the backing of 1mm sterling and heating it from underneath, it refuses to melt completely.
It's "stuck" but not completely bonded. I can see light at certain points.
I'm using Auroflux.
I thought perhaps I'd used the solder too thick (even though I had run it through a mill already), so tried again
after beating with a hammer and have the same result (slightly better but not perfect)
As I want to enamel the piece I'm stuck.
What can be the matter?
Any help gratefully received.

[Dennis]

Auflux/Auroflux is known to get exhausted rapidly, so the first thing to do now if you have pickled it is to boil it up with soda crystal or baking soda solution and then with plain water.
Then drench it in borax and re-heat. If the solder won't flow now, the piece has become too big for your torch and you need to use a hotter torch or two together. Dennis.

[NickD]

Auflux/Auroflux is known to get exhausted rapidly, so the first thing to do now if you have pickled it is to boil it up with soda crystal or baking soda solution and then with plain water.
Then drench it in borax and re-heat. If the solder won't flow now, the piece has become too big for your torch and you need to use a hotter torch or two together. Dennis.

Borax?
OK I'll, need to order that.And heat the whole piece? It's only about 2 x 1"
The last time I heated it to infinity and beyond(!) and I didn't think it could take it any more.Bright orange.
I didn't know that about Auroflux.
It didn't seem possible it wouldn't "go".
Thanks so much

[enigma]

I don't know why this happens Nick but it has happened to me before too even with plenty of heat from the Smiths torch.
I found that I got it to flow eventually after pickling, drying and reapplying plenty of flux- I also use Auroflux.
I haven't heard about the borax before though so that may well work better.

[NickD]

I've just ordered some. It seems to be a rapidly disappearing species though.