Most of what I see as what goes for mortar analysis is to try to match 
color and size of aggregate to the existing in hopes to identify 
commercially available materials to come close to what is seen in the 
original mortar. If one goes with the general assumption, as I do, that 
a weathered joint exposes the aggregate and that the aggregate makes for 
a more durable color than the binder (ruling out historically tinted 
mortars) it is at least one step to get a mortar that does not glaringly 
stand out from the existing. If one is doing museum quality conservation 
a more exact analysis is certainly appropriate, but for the vast 
majority of 'maintenance' of older masonry structures, and in a place 
like NYC where there are so many of them and so many contractors with a 
truck that says "RESTORATION" on the side of it... to even think to try 
to match the aggregate in color and size is a big step.

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