Cheers, it really does need painting, it's been a long build and even the nickel silver is beginning to tarnish, mostly where the soaps and cleaning agents attack the solder and fluxed areas. I'm still looking for a cleaning agent that cleans and doesn't tarnish as a by product.
Rob, I've used Viakal in the past and found it to be one of the most aggressive, I tend to use Limelite these days but even that creates staining long term. I've used pretty much all of the kitchen cleaning agents and all tarnish the base material.
, it's smooth and once painted is invisible, but in bare metal they look awful.
never been called that, competent dabbler more like 
The pipework is a test in patience and fortitude, there is no other way to describe it
Yes I've heard that before but never had any problems, my go to painter hasn't either; that could be down to both of us mixing our own industrial cellulose etch primer as a base coat.Phoenix make this point in their painting guide for the etch primer:
'DO NOT use washing up liquid as it contains a chemical coating to ensure that crockery etc. ‘sparkles. Whilst this coating is harmless for most purposes it reacts with paint and primers causing problems for the unwary modeller.’.
Not sure if that helps or hinders?
Tony, for years I used the exact same flux and am now using the one recommended on WT Safety Solder Flux a few months back (I bought a litre which will last a few years, I still have two bottles of the BOG stuff as a reserve) as the BOG stuff was getting hard to come by.
, don't knock yourself, I've followed your models for years and they were and still are a rock solid benchmark 
and as we all know, clean models mean diddly squit once painted. So long as they are mechanically clean and smooth, then eliminating the tarnishing is nowt more than a folly 
Appreciated, I'll keep looking, there must be some somewhere as they appear to be a popular subject.
there's going to be quite a lot of scratch building and I may just not bother and get new etches drawn up, especially for the tank sides, the kit ones are 0.7 mm and you have to blind punch all the rivets from a paper overlay; then, bend them at the front to meet the boiler 
.
Dave,Apologies if you already know this but just throwing some thoughts around
I would use tepid rather than hot water if you reside in a hard water area. Hot water increases the release of limescale which may (as daft as it sounds) leave trace deposits on the model. In addition limescale contains traces of iron which could be the brown staining at the solder joints.
If you do have a water softener installed this may not totally remove the limescale and other trace elements.
The harder the water the more soap/detergent is required for cleaning. I remember when we lived near Ipswich many moons ago the water was quite hard as the kettle was forever furring up.
After scrubbing and cleaning the model with the detergent you normally use I would rinse the model under the cold tap to remove the detergent. Before this I would prepare a final rinse of tepid or cooled boiled water from the kettle as this would have most of it's limescale and trace elements removed. Then shove the model in a warm atmosphere to dry i.e. airing cupboard.
I believe the natural oxidisation process of tarnishing has been covered previously which as we know is affected by atmospheric conditions but this could, at a chemical level, be hastened by any trace elements left on the model after cleaning to act as a catalyst for this process. Also, as we apply heat to the kit during assembly we are altering the structure of the metal at a molecular and atomic level in these areas. All subtle changes which may alter the oxidation process of these previously heated areas.
