Indeed we may consider as a general principle that the larger the
interspaces of the ground, plane, or field of the pattern, the lighter
in tint they should be, or the necessary flatness is apt to be lost.
Relief in pattern design may be said to be adding interest and richness
without losing the flatness and repose of the design as a whole. When
pattern and ground are fairly equally balanced in quantity the ground
may be rich and dark, and darkest as the interstices, where the ground
is shown, become less. The figure of a pattern relieved as light upon a
dark plane, as a rule, requires to be fuller in form than dark-figuring
upon a light ground.

[Decorative Relief]

In decorative work the use of contrast in the relief of parts of a
design is often useful and effective, as, for instance, the dark shading
or treatment in black or flat tone of the alternating under side of a
turn-over leaf border.

The decorative value of this principle is recognized by heraldic
designers in the treatment of the mantling of the helmet, which in
earlier times is treated simply as a hanging or flying strip of drapery
with a lining of a different colour, by which it is relieved as it hangs
in simple spiral folds. This ornamental element became developed by the
designers of the fifteenth and sixteenth centuries into elaborate
scroll designs springing from the circlet of the helmet and surrounding
the shield: but the principle of the turned-up lining remained, often
variegated and enriched with heraldic patterns (see illustrations, pp.
172[f094a], 173[f094b]).*

[*] The increased importance given to the mantling in later times
may have been due to the disappearance of the housings of the
knight's horse and his surcoat, which originally displayed his
arms and colours. The mantling of later times displayed the
heraldic colours of the knight, when, being clad in plate armour,
there was no other means of displaying them except on the shield.
Decoratively, of course, the mantling is of great value to the
heraldic designer, enabling him to form much more graceful
compositions, to combine diverse and rigid elements with free and
flowing lines and masses, and to fill panels with greater
richness and effect, whether carved or painted, or both.

[Illustration (f094a): Decorative Relief: Counterchange, Treatment of
Mantling, Fourteenth and Sixteenth Ce