Guido taught at Rome, and gave his pupils, as we have stated, to that city. He educated still more for his native place, where he opened a school, frequented by more than two hundred pupils, as we are informed by Crespi. Nor are we by this number to measure the dignity of his character as a master. He was an accomplished head of his school, who, in every place, introduced into the art a more sweet and engaging manner, entitled in the times of Malvasia the modern manner. Even his rivals took advantage of it, the fact being indisputable that Domenichino, Albano, and Lanfranco, along with their best disciples, derived that degree of delicacy, in which they sometimes surpass the Caracci, from none but Guido. He would not permit the scholars in his studio to copy in the first instance from his own works, but exercised them in those of Lodovico, and the most eminent deceased masters. It is conjectured also by Crespi, that he grounded his scholars in the principles of the art of imitation, and all the first requisites, without reference to the minutiæ, which are easily acquired in the course of practice. Guido particularly prided himself on Giacomo Semenza, and Francesco Gessi, whom he thought equal to any masters at that time in Bologna. He employed them in that chapel of the cathedral at Ravenna, a perfect miracle of beauty, and gave them commissions from the court of Mantua and Savoy, assisting them also, both at Rome and his native place; in return for all which he was repaid by Semenza with gratitude, but by Gessi with bitter persecutions. He was followed by both in point of style, and specimens are to be seen in some choice collections.
Semenza emulated Guido in both his manners, and displayed more correctness, erudition, and strength. His pictures at Araceli and other places sufficiently distinguish him from the immense crowd of fresco-painters at Rome. There too are many of his altar-pieces, none more beautiful, perhaps, than the S. Sebastian, at S. Michele in Bologna. Gessi surpassed him in spirit, invention, and rapidity, for which last quality even Guido envied him. This enabled him too, from the first, to vary his works in point of manner until he hit upon the right one, as in his very beautiful St. Francis at the Nunziata, little inferior to Guido, as well as in several others conducted in his earlier and best days. To these he was indebted for his name of a second Guido; but subsequently he abused his talents, as is the case with those who are held in slight esteem for performing much and rapidly. Thus Bologna abounds with his pictures, in which, with the exception of their fine character and much delicacy, there is nothing to commend; his pictures are cold, his colouring is slight; the shape and features are often too large, and not seldom incorrect. He is known to have invariably affected the second manner of Guido, and hence he is always more feeble, dry, and less harmonious than his master. By these distinctions are the differences between salesmen and purchasers usually decided, as to whether such a piece be a poor Guido or a Gessi.