Brian,

The best thing about acid digestion is that it's cheap and quick. I confess to using it for initial screening of specimens, when I want a clue as to whether they are straight lime (or I should say predominantly lime) as opposed to something hydraulic. But I would never have the gall to issue a report claiming that this method is very accurate or definitive, as was done in the recent case in question. Too many "conservation labs" are still relying on this method.

Beyond that, the samples have to go out to an expert for thin-sectioning and polarized light microscopy for basic binder identification. Part of being an expert is being able to recognize that the portland cement you just found in your 1876 mortar sample could not have been produced in 1876, and represents a more recent intervention. Try figuring that out with acid digestion.

Mike E

> Now, now Mike. 
> 
> I find acid digestion to be a great teaching tool, if it is not a good stand alone method for mortar analysis.  I think that your previous point that the samples are only as good as the guy taking them is right on the money. Samples must be collected with a complete understanding of the masonry process that was used on the structure. Anything less is a waste of time. 
> 
> Brian  
>

 

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