IDENTIFICATION OF DYES ON OLD TEXTILES
FIGURE 1 shows the lakes formed by the yellow natural dyes that are most frequently encountered: weld extract, quercitron, Persian berries, old fustic, turmeric, and kalama. Shown are the colors of the aluminum, iron, copper, and uranium lakes of the dyes just mentioned, and also the colors of the tin lakes both before and after treatment with ammonia. In practice the dyes are usually in the form of the aluminum lake in the fabric, so that boiling with alum solution seldom changes the yellow shade, except perhaps to brighten it through soil removal. The lakes whose colors differ distinctly from the others are marked with a cross.
Lakes of yellow natural dues.
Looking at Figure 1 one can see that only the tin lakes of quercitron and turmeric are orange. When the tin lake of turmeric is treated with ammonia it turns brown at first and then becomes yellow when washed with water. That of quercitron turns deep orange when heated with ammonia. These observations are sufficient to distinguish the two dyes from the other four. Old fustic and kamala both have orange-yellow tin lakes, but can be distinguished by the behavior of these lakes when treated with ammonia and also by the colors of their iron and copper lakes. Weld extract and Persian berries both have yellow tin lakes, but can be distinguished particularly by the behavior of these lakes when treated with ammonia and by the different colors of their copper lakes.