Thanks, all. Some good ideas here
and Raimond, too funny
I've decided it's a bit tricky for someone of my skill level, to attempt something of this size. I'd hate to ruin it and present him with a melted mess of gold and glass.
The boro tube idea is great, too, but probably a lot of work for my little torch. I did think of blowing a soft glass vessel, (wants a puffy heart shape), because he wants the heart in the style of my 'cave' beads, with windows to pretty things like Goldstone and silver glass amongst swirls of silvered Ivory on the outside. No way I could do silvered Ivory boro - or even fit the nugget through my 10mm blowpipe-sized top hole, for that matter
I'd put my concerns to the customer about the fuming, compatibility, melting point etc etc etc, and eventually we've come to an agreement on a method.
I suggested I could try to mimic a gold nugget with a Goldstone chunk, carefully encased. I have to see, though, whether I can still gravity-shape a heart without distorting the Goldstone. If I can, then we're sweet
Thanks again, all. Much appreciated.