The four main devices (symbols) in the John blazon are the bar, bezant, Cornish chough and wilk shell. 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 bar is a thin, horizontal stripe across the centre of the shield 6A Glossary of Terms used in British Heraldry, J.H. Parker, Oxford, 1894, Entry:Bar, usually in groups of two or three (any more and there would be confusion with barry, a treatment of horizontal lines of alternating colours). Bars can be a distinctive and easily recognised device, early examples include those awarded by Henry III of England to the family MAUDYT Argent, two bars gules.
For easy recognition of the items on a coat of arms, and hence the quick identification of the owner, bold simple shapes are best. Hence, simple geometric shapes are often used for this purpose 7A Complete Guide to Heraldry, A.C. Fox-Davies, Bonanza (re-print of 1909 Edition), New York, 1978, P146xz`, and the bezant Is a typical example of this, and in British Heraldry always takes the tincture or. It shares the same root as the name Byzantium, being associated with the gold coin of that city and indeed, in some heraldic traditions is represented as a coin-like disk in perspective. Wade suggests that the use of this device refers to ” one who had been found worthy of trust and treasure.” 8The Symbolisms of Heraldry, W. Cecil Wade, George Redway, London, 1898 P122
Birds of great variety occur throughout heraldry, at least in name 9A Complete Guide to Heraldry, A.C. Fox-Davies, Bonanza (re-print of 1909 Edition), New York, 1978, P233. The Cornish Chough is a member of the crow family and is often depicted as black with red or orange beak and legs. 10A Glossary of Terms used in British Heraldry, J.H. Parker, Oxford, 1894, Entry:Cornish chough Wade gives it the role of “king of crows” and believes that its use denotes a “man of stratagems”. 11The Symbolisms of Heraldry, W. Cecil Wade, George Redway, London, 1898 P82