One of the many things I learned on the course was that silver solder is used in place of brass brazing sometimes. Usually because the part is stainless steel or because the tube wall is too thin (brazing temps would damage it) to heat up to the temps required to melt brass and induce the capillary action. Here’s a useless fact: it takes around £150 worth of silver solder alone to build an entire stainless steel frame……fascinating.
Whilst sandblasting was pretty effective at removing most of the dried flux and other crap there was still the odd bit of excess brass and spatter left behind. All of this has to be filed and sanded by hand to make the frame silky smooth to paint.