I have a rather nice old hand-built 531 frame and fork that I'd like to have repainted. Some companies offer bead-blasting to prepare it, but others offer chemical stripping.
Is this as good as bead-blasting for steel; does it offer any advantages?
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Both processes serve to remove paint coat from your frame. The only difference is that bead blasting may (or may not, depending on the medium used) scratch/damage the metal surface of your frame.
If you don't like that possibility, then you can opt for chemical stripping (especially if they'll treat the frame after for effective coat adhesion), but I'd consult with the establishment first on how your steel frame would react to the chemicals.
With that said, the link you gave also advertised giving treatment to your frame to prevent under-coat corrosion, so that's a nice touch for me.
Abrasive blasting could use a variety of different materials, from harsh glass beads or powders through sand/silicates, to something quite gentle like walnut shells or sawdust.
The effectiveness comes down to the operator's skill and understanding of the surface and existing paint job.
If your bike was given a lot of coats of paint (primer, undercoats, top coats, and clearcoats) then there may be a dozen layers of paint. If it was a budget paint job there may be one layer.
One advantage to blasting is that it will leave the raw surface with microscopic indents which will help your primer coat or undercoat to key into the surface, improving adhesion of the initial coating.
I doubt that chemical cleaning will leave as good a surface. However Chemical soaks will get into corners better than large particle abrasive blasting. Small particle blasting will do corners just fine.
Overall cost is probably the deciding factor, and do remember that a frame stripped of paint is already rusting. You need to get a first layer on as soon as possible. Most blasting companies will flash it over with zinc spraypaint as part of the job, though check this.
Remember the frame needs prepping too - meaning bosses and threads need consideration. You have to remove everything including headset races and anything chrome.
Its reasonable to chase all the threads afterward too, but a pair of BB taps is expensive, so consider getting a LBS to do all this.