The two main devices (symbols) in the Joule blazon are the martlet and fesse. The two main tinctures (colors) are sable and argent.
Sable, the deep black so often found in Heraldry is believed to named from an animal of the marten family know in the middle ages as a Sabellinœ and noted for its very black fur 1A Glossary of Terms used in British Heraldry, J.H. Parker, Oxford, 1894, Entry:Sable. In engravings, when colors cannot be shown it is represented as closely spaced horizontal and vertical lines, and appropriately is thus the darkest form of hatching, as this method is known 2Boutell’s Heraldry, J.P. Brooke-Little, Warne, (revised Edition) London 1970, P 26. Although it may seem a sombre tone, and does indeed sometimes denote grief, it is more commonly said to represent Constancy 3The Symbolisms of Heraldry, W. Cecil Wade, George Redway, London, 1898 P35.
Argent is the heraldic metal Silver and is usually shown as very pure white. It is also known more poetically as pearl, moon (or luna) 4Understanding Signs & Symbols – Heraldry, S. Oliver & G. Croton, Quantum, London, 2013, P53. In a sketch or drawing it is represented by plain, unmarked paper 5A Glossary of Terms used in British Heraldry, J.H. Parker, Oxford, 1847, P11.
The martlett is by far the most common bird to appear in British Heraldry, perhaps only equalled by the eagle, however it is not a species ever to be found in an ornithologists handbook! The word itself is though to have come from the French word merlette, the female blackbird and itself a similar type of charge used in French Heraldry. 6A Glossary of Terms used in British Heraldry, J.H. Parker, Oxford, 1894, Entry:Martlet. Over time the image has become quite stylised, without visible legs or distinctive feathers. Wade suggests that this representation arises from “the appearance of the bird of paradise to ancient travellers” 7The Symbolisms of Heraldry, W. Cecil Wade, George Redway, London, 1898 P79. Other bird species may be named in coats of arms (cornish chough is a frequent example) but in actual execution their appearance is often indistinguishable from the martlet.
The fesse (also found as fess) is one of the major ordinaries to found in heraldry, being a bold, broad, horizontal band across the centre of the shield. It may originally have arisen from the planks of which a wooden shield can be constructed, the centremost plank being painted a different colour 8A Glossary of Terms used in British Heraldry, J.H. Parker, Oxford, 1894, Entry:Fesse. It is instantly recognisable as a symbol, for example the arms of COLEVILLE granted during the reign of Hery III are simply or, a fesse gules. With this clear association with the construction of the shield itself, Wade believes that the fesse can be taken to be associated with the military, as a “girdle of honour”.