Archaeomagnetic dating of seven archaeological fireplaces in the Netherlands

The palaeomagnetic directions of seven Dutch fireplaces are compared with the archaeological age estimates which range from the first to the 17^th century AD. A comparison with the British master curve of secular variation for archaeomagnetic dating results in a refinement of the archaeological age estimates in two cases, while four other archaeological age estimates can be confirmed. For one fireplace only one sample is reliable, resulting in a very poorly defined archaeomagnetic age of 2 to 3 centuries younger than the expected age (i.e. late Middle Ages). On the other hand, accepting the archaeological age estimates, the palaeomagnetic directions can contribute to the database that is used to construct the British secular-variation master curve. We applied the classification grades proposed by Tarling & Dobson (1995) which range from unreliable (grade 1) to reliable (grade 5). Three fireplaces have grades 5, one has grade 4, one grade 3, one grade 1 and for one case no grade was assigned.