Hello again, glad the other reply helped.

The paints used on furniture then would have been largely mineral and some vegetable pigments bound/tempered with egg (egg tempera) or oil, usually linseed oil, and they were widely applied to wood in period. I’ll continue on the nature of these pigments and paints shortly. We are lucky enough to have many surviving examples of painted furniture survive today, and I have been personally interested in surviving examples of painted boxes and chests. Some of these would have been richly decorated with ormenatal devices and patterns, and often they would have been decorated with the arms of the family who owned the piece, for example there is a large oak chest in the Burrell Collection, Glasgow which is presumed to have been owned or somehow associated with Richard de Bury (1281-1345) because of the painted arms on the inside of the lid.

We’re lucky enough to have lots of documentary evidence of what painting materials and techniques were in period, some notable examples include Cennino d'Andrea Cennini's Il Libro dell'Arte, The Mappae Clavicula, Theophilus’s De Diversis Artibus and the manuscripts of Jehan Le Begue.

Wooden surfaces would have needed to have been prepared with gesso to give a smooth working surface to gild and paint on. Gesso is like a thick white plaster or paint, usually made with chalk or gypsum plaster, and often this was applied on a layer or two of glue lined with linen or parchment which is why when the paint cracked it still stayed in place. Again Cennini is great for evidence of how this was made and applied.

Colours came from mineral and vegetable sources and could have materials like alumina or chalk added to affect transparency and opacity. Egg as the binding agent was used sometimes with gum Arabic, or maybe a little sugar or honey to help the paint not become too brittle. Gum Arabic helped give the paint a shiny appearance too. Egg was used extensively in early period, gradually replaced by oil after the 15th century. This is not quite the oil paint we are familiar with today, merely that the pigments were mixed with different oil (usually linseed) or mixtures of oil and resins.

Earth pigments of the time would have included Terre Verte, a green earth from galuconite and celadonite and the briwn-yellows and brown-red of ochre and burnt ochre. Minerals that were commonly used in pigments include Ultramarine which was expensive as it is made by grinding up lapis lazuli and imported mostly from Afganistan. It was highly prized and definitely would have been seen as a indictor of status. Azurite was a cheaper alternative. Malachite produced a distinctive green and Orpiment a range of yellows that are poisonous and carefully avoided by modern painters for the most part. The sources above also include recipes and methods to make lead white and red lead, lead tin yellow and vermillion (red) from mercuric sulphide from cinnabar (also very much to be avoided today, but the methods to make them are fascinating! Cennini's work includes a warning that one should use one's "least favourite apprentice" when working with mercury) Verdigris made a blue green.

The materials I mentioned before for dyeing were also often used to make pigments, including kermes, brazilwood, logwood, indigo and woad. Plant matter and berries could be used to make lakes but these were not really used on furniture.

Staining furniture with oil darkened with walnut or oak galls was also a notable feature of furniture decoration as were wood inlays. There are many tricks to colour and stain wood for inlaying in period sources. Gilding with gold leaf would also have been reasonably common on the higher quality, more expensive end of the furniture market.

For more extensive reading these might help:

Gerald W.R. Ward The Grove Encyclopedia of Materials and Techniques in Art

Daniel V Thompson The Materials and Techniques of Medieval Painting

Mary P. Merrifield Medieval and Renaissance Treatises on the Arts of Painting.