Ibo Ortgies Vallotti in the Province of Groningen: On restoring temperaments
Het ORGEL 98 (2002), nr. 5, 27-39 [summary]

Temperament is a decisive element of the sound concept of an organ and its maker. In recent years well-tempered temperaments based on 1/6th of the Pythagorean comma, such as the related systems of Vallotti and Young, have been frequently used in organ restorations.
The relevance of these temperaments, however, is highly doubtful 
for organs of the Arp Schnitger tradition, which lasted in the province of Groningen until after 1800. Investigation of several organs shows that the Schnitger tradition stayed with meantone temperaments at first, and only slowly turned to well-tempered systems. Division of the comma into larger portions was favoured at this time, probably still reflecting the point of departure, which was meantone temperament with pure major thirds. This is totally in line with the development in greater parts of North Germany and the rest of The Netherlands.
The F.C. Schnitger/Freytag-organ (1797) in Bellingwolde deserves special attention: the irregularly modified meantone temperament which was found during the last restoration has been changed to a more regular, modified meantone temperament, in which form it serves now as an argumentative basis to promote well-tempered (non-meantone) 1/6-comma-systems (Vallotti or Young) for organs of the later Schnitger-tradition. The organs in Midwolda (1772) and Bierum (1792, which originally had a 1/6-comma meantone temperament), have been tuned for the second 
time since restoration, ending up in a Vallotti- or Young-temperament. Even the most recently restored Arp Schnitger organ, in Uithuizen (1701, changed by A. A. Hinsz in 1785), claimed as one of the 'most authentic organs of Arp Schnitger', was tuned in the Vallotti temperament; to this end the Rugpositiv had to be retuned, because it had been given a modified meantone temperament in the first phase of the restoration (1987).
Ortgies questions strongly the arbitrary restoration practice in this matter, which seems to be based on personal preferences more than on respect for original findings about temperaments. Making available the documentation about these original findings would help to avoid choosing temperaments that are inappropriate to the respective era, region and tradition of organ building.