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Darryl,
The requirement here when mixing crushed walnut shells with the paint is to get a paint with the highest level of durability, not necessarily the most non reflective black surface. Krylon certainly works well and I have used it before. I have also used White Night flat black epoxy paint and it works equally as well as Krylon and is very durable. The last thing you want in this situation is pieces of paint or walnut shell flaking off onto the primary mirror.
The object of the exercise is to have a non reflective paint combined with another medium which breaks up all available angles of incidence for the light to reflect off. The crushed walnut shells having no defined shape or form do this very effectively as they essentially point at all different angles all over the place and block all available light paths. The crushed walnut shells are doing the majority of the baffling work, not the paint. Of course having a very non reflective paint in this situation can't hurt. For the same reason, felt or flocking paper IMO is the best choice because it is made up with minute fibres pointing all over the place which break up the angles of incidence for the light to reflect off. Plain and simple blue felt, green felt or any colour felt, would do an equally good job of baffling the scope as would black felt. It is the medium that is non reflective not the colour. We use black felt as a matter of choice because of the mental association of black being non reflective. Plus it looks the part.
If you are not going to mix walnut shells into the paint, then your advice to use Krylon is correct. It is the most non reflective black paint available. Krylon on its own without the walnut shells will improve the non reflectivity over the standard scope, but it doesn't do nearly as good a job as felt, flocking paper or paint mixed with walnut shells and isn't what I would be doing. When you mix the walnut shells into the paint you need the walnut shells so thick they touch each other when you paint the surface. One piece of walnut shell here and there doesn't do squat.
My first choice to properly baffle the scope is the self adhesive craft flocking paper available from Spotlight Stores. It costs about $40 for enough to do an entire 12" scope. Protostar in the USA aslo sell it but it will cost a lot more than buying it from spotlight. It comes in pieces the size of an A4 piece of paper and costs about $2-00 a sheet from Spotlight. It has a very pale blue backing sheet onto the self adhesive. Tip: The glue on this stuff sticks like anything and once one piece touches the other or a piece doubles over and touches itself they are stuck. Hence cut the sheets in half before peeling off the backing paper making them easier to handle and minimising the risk of doubling it onto itself and ruining the sheet. Overlap each sheet when applying by about 4mm. This flocking paper will do an infinitely better job than krylon without walnut shells.
The unknowing think its the colour and non reflectivity of the paint that properly baffles the scope; when in fact its the non reflectivity of the surface medium itself and colour matters not near as much, if the job is done properly
Cheers,
John B
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