Petrography lower if wholly or partly vitreous. The specific gravity of the more common rocks range from about 2.5 to 3.2. Archaeologists use petrography to identify mineral components in pottery. This information ties the artifacts to geological areas where the raw materials for the pottery were obtained. In addition to clay, potters often used rock fragments, usually called "temper" or "aplastics", to modify the clay's properties. The geological information obtained from the pottery components provides insight into how potters selected and used local and non-local resources. Archaeologists are able to determine whether pottery found in a particular location was locally produced
The Gothenburg Study of Children with DAMP conclusion which does not need strengthening by what could have been found in the destroyed research material". (Another problem is the boy:girl ratios in the study; the ratio in the control group is 1:1, whereas the ratio in the index groups is 4:1.) The major Swedish newspapers have had tens of stories on the controversy: Dagens Nyheter, Svenska Dagbladet, Göteborgs-Posten, etc. There was also a one-hour program about DAMP on Swedish TV that discussed the controversy over Gillberg's Gothenburg study at length. In Norway, the newspaper Dagsavisen ran a series of critical stories. The Gothenburg Study of Children with DAMP