I had another go at some soldering earlier this evening, in preparation for making up the handrails for the Toad brake van. The main question that had been bothering me was how to hold everything securely and squarely in place while soldering. The solution I've come up with (and which is probably obvious to anyone who has done any soldering at all) is to create a makeshift jig allowing each rectangular 'set' of handrails to be pre-assembled and held securely in place while soldering.
I drilled four holes in a piece of wood to locate the handrail fastenings in, and used thin strips of plasticard fixed down with double sided tape to raise the handrail wire off the surface of the wood by .5mm or so. The wire was carefully lined up with the corner fastenings using needle nosed tweezers and secured with small pieces of Carrs hot tape.
The joints were given a drop of Carrs yellow label flux (not sure how necessary this is when using solder paint? is the flux simply to help the solder flow into the joint or does it have anything to do with the strength of the joint?), then a drop of solder paint was applied to each corner/joint with a cocktail stick before applying the heat for a second or two. Initially I didn't use enough of the solder paint (actually I'd failed to shake/mix it thoroughly enough so I was only applying a watery residue) - I discovered that you can actually apply a fairly liberal blob of the stuff since as soon as you apply the heat most of it burns up. After a couple of minutes I removed the assembly and washed it with some washing up liquid and warm water.
The joints appear to be secure and there aren't any noticeable blobs of solder so I think the experiment was a success. Just need to get on and make all those handrail fastenings.....