Tondo derives from rotondo, the Italian word for circular. Circular panel paintings (tondi) became popular in Italy about the middle of the 15th century, particularly in Florence.
Predella is the Italian term for the long horizontal structure at the base or ‘foot’ of an altarpiece. They usually depict narrative scenes which are related to, or expand upon, the subject of the larger images above.
Bole is a kind of clay, which is usually red due to the presence of iron oxide (as seen on the left-hand side above). It is used as an under layer prior to the application of gold leaf (as seen on the right-hand side). It has the effect of making the gold appear richer in tone.
Water gilding is one of the most common types of gilding. It refers to the process of applying a thin layer of gold to solid surfaces. It usually takes place before painting. The advantage of water gilding is that the gilded surface can be polished and decorated afterwards.
Mordant gilding is a common type of gilding, where gold leaf is laid over an adhesive mordant, such as oil. It typically takes place after painting. Mordant gilding produces a matte finish, as the gilded surface cannot be polished afterwards.
Sgraffito (from the Italian graffiare: to scratch) is a form of decoration made by scratching through a surface to reveal a lower layer of a different colour. The term typically refers to a type of façade decoration in plaster or stucco that was prevalent in 15th- and 16th-century Italy, and can also be used to refer to a technique frequently used in early Italian panel paintings.
Powdered gold can be mixed with a binder such as gum arabic to make a gold paint. Shell gold has a fine granular texture and appears quite dull. It is typically applied with a brush and used only for areas of fine decoration, as in the example above, where it has been used to give the effect of the sheen of silk.
Gesso is the Italian term for the white mineral ground or preparatory layer that ensures a smooth surface for painting or gilding on wood. It was also used to prime canvas. A coarse lower layer is applied (gesso grosso), followed by a finer upper layer (gesso sottile). It has to be scraped and sanded to make it absolutely smooth.
Pastiglia is an Italian word which describes the soft low relief in gesso normally used as a ground for gilding, either within the painted surface (specially Italian panel paintings of the 14th and 15th centuries) or on frames.
Art books to enjoy this Christmas
While you’re here...
Look out for special gold labels next to paintings in the Sainsbury Wing, and give your selfies an Old Master sparkle with our gold frame filter on Snapchat.