It follows from this that your convention must be your own, and not borrowed from other times and peoples; or, at the least, that you must make it your own by thoroughly understanding both the nature and the art you are dealing with.  If you do not heed this, I do not know but what you may not as well turn to and draw laborious portraits of natural forms of flower and bird and beast, and stick them on your walls anyhow.  It is true you will not get ornament so, but you may learn something for your trouble; whereas, using an obviously true principle as a stalking-horse for laziness of purpose and lack of invention, will but injure art all round, and blind people to the truth of that very principle.

Limitations also, both as to imitation and exuberance, are imposed on us by the office our pattern has to fulfil.  A small and often-recurring pattern of a subordinate kind will bear much less naturalism than one in a freer space and more important position, and the more obvious the geometrical structure of a pattern is, the less its parts should tend toward naturalism.  This has been well understood from the earliest days of art to the very latest times during which pattern-designing has clung to any wholesome tradition, but is pretty generally unheeded at present.

As to the limitations that arise from the material we may be working in, we must remember that all material offers certain difficulties to be overcome, and certain facilities to be made the most of.  Up to a certain point you must be the master of your material, but you must never be so much the master as to turn it surly, so to say.  You must not make it your slave, or presently you will be a slave also.  You must master it so far as to make it express a meaning, and to serve your aim at beauty.  You may go beyond that necessary point for your own pleasure and amusement, and still be in the right way; but if you go on after that merely to make people stare at your dexterity in dealing with a difficult thing, you have forgotten art along with the rights of your material, and you will make not a work of art, but a mere toy; you are no longer an artist, but a juggler.  The history of the arts gives us abundant examples and warnings in this matter.  First clear steady principle, then playing with the danger, and lastly falling into the snare, mark with the utmost distinctness the times of the health, the decline, and the last sickness of art.

Allow me to give you one example in the noble art of mosaic.  The difficulty in it necessary to be overcome was the making of a pure and true flexible line, not over thick, with little bits of glass or marble nearly rectangular.  Its glory lay in its durability, the lovely colour to be got in it, the play of light on its faceted and gleaming surface, and the clearness mingled with softness, with which forms were relieved on the lustrous gold which was so freely used in its best days.  Moreover, however bright were the colours used, they were toned delightfully by the greyness which the innumerable joints between the tesserae spread over the whole surface.