However, to better understand physicochemical techniques it's best to recall how a painted work is made, e.g. an illustrated icon. After choosing the wood for the artwork, the iconographer applies "primer" to its surface, which is a white mixture used to treat the surface. On this white layer the paint that forms the image is applied with a brush. After completing the painted image, the work is finalized with a coat of varnish. Paint was produced quite differently in the past than it is today. Painters used to use paint made of powder pigments that came in granule form. In order to turn these powders into colors that could be applied with a brush, it was mixed with various liquids, such as egg or oils. In physicochemistry these liquids are called "binders" or carriers. Some physicochemical techniques can be applied without any contact with the work, e.g. either simple or more specialized photography of the work. Other physicochemical techniques require the collection and of microscopic pieces ("samples") for analysis, known as sampling. The Laboratory of Physicochemical Research of the National Gallery has excellent imaging technology, including a camera, a multispectral imaging camera, a metallographic microscope, a gas chromatograph and infrared spectroscopy tools. This equipment contributes significantly to the study and conservation of paintings and sculpture. The process is explained in detail below.