Why do you want to do it by yourself - can't you buy ready one? I recall some type of silver paint that was used for covering of hot metal in chimney/ventillation ducts, no idea if it still in use.

What pigment do you want to use? Aluminum powder will be probably the best, although you may have troubles buying it, as it can be used to make explosives.

just want to know I there is anyway of stopping or reducing the separation?

If it is thinned the separation is just a gravitational sedimentation, I doubt you can do much about it. Does shaking helps?

When pH is raised...

...Al dissolves.

Al dissolves at elevated pH?   What effect would this have on a paint Borek?  Surley when the 'solvent'  evapourates the Al would be left coated on the substrate?    

It will dissolve chemically, so once the paint dries there will be no metallic Al but some salt - and it will be no longer silver in color.

OK just something to try, may or may not work, but what about a dash of washing up liquid  or soap  - -  these are surfactants that are cheap and readilly available.   If you need something a bit more sufisticated then you'll need something else, but soap is a good start I rekon.

(take my snacks away if this is a really daft sugestion, but I've found washing up liquid does the same job as many a high tech surfactant  - -     oh wait!!   I don't have any snacks at all!!!!!     )