Shot blasting

if you can get your hands on a good compressor/lock up garage, I have a spot blasting gun that works on 'normal' sand that works at about 100-120 psi that would do your frame ok. if you would like to borrow it then shout, (I'm in hackney). if you then wanted to spray it I have refinishing guns too.

Normal sand is too coarse for blasting a frame. I did mine using vegetable abrasives which we used for blasting glass lenses etc. Overkill but gave a nice finish.

I would pack the BB/headtube out with news paper and any other small holes with matchsticks first.