In 1845 we find him installed at Paris, though no longer in the army.  Then it was he began to design.  He became contributor to many periodicals, among the rest the Illustrated London News and Punch.  For the former journal he went to the Crimean war as accredited art correspondent.  The portfolio containing the Crimean set is now most sought for by his admirers.  He is said to have originated the expression “taken on the spot,” in the title of one of his instantaneous sketches.  Few draughtsmen could boast his sure eye and manual dexterity.  The Balaklava illustration is as striking in its way as Tennyson’s lines, though containing less of poetic heroism and more ugly realism.  Like the trained reporter that he was, Guys followed a battle, recording the salient incidents of the engagement, not overemphasising the ghastliness of the carnage, as did Callot or Goya or Raffet, but telling the truth as he saw it, with a phlegm more British and German than French.  Though he had no Dutch blood in his veins, he was, like Huysmans, more the man of Amsterdam than the man of Paris.  He noted the changing and shocking scenes of hospital life, and sympathy without sentimentality drops from his pen.  He is drily humorous as he shows us some plumaged General peacocking on foot, or swelling with Napoleonic pride as he caracoles by on his horse.  And such horses!  Without a hint of the photographic realism of a Muybridge and his successors, Guys evokes vital horses and riders, those seen by the normal vision.  The witching movement of beautiful Arabian steeds has not had many such sympathetic interpreters.

In Turkey he depicted episodes of daily life, of the courts of the Sublime Porte itself, of the fete of Bairam, which closes the fast of Ramadan.  His Turkish women are not all houris, but they bear the stamp of close study.  They are pretty, indolent, brainless creatures.  In his most hurried crayons, pen-and-ink sketches, and aquarelles Guys is ever interesting.  He has a magnetic touch that arrests attention and atones for technical shortcomings.  Abbreviation is his watchword; his drawings are a species of shorthand notations made at red-hot tempo, yet catching the soul of a situation.  He repeats himself continually, but, as M. Grappe says, is never monotonous.  In love with movement, with picturesque massing, and broad simple colour schemes, he naturally gravitated to battle-fields.  In Europe society out of doors became his mania.  Rotten Row, in the Bois, at Brighton or at Baden-Baden, the sinuous fugues of his pencil reveal to succeeding generations how the great world once enjoyed itself or bored itself to death.  No wonder Thackeray admired Guys.  They were kindred spirits; both recognised and portrayed the snob mundane.