‘Tiepolo,” the title of a new exhibition in the Robert Lehman Wing of the Metropolitan Museum, is at once scrupulously accurate and entirely deceptive. For the show gives us two Tiepolos, Giambattista and Giandomenico, father and son, respectively, represented by about 65 drawings that belong to the Lehman Collection. But the distribution is hardly equitable. By my count, the son’s contributions outnumber the father’s by about two to one. And since the father was surely the greater draftsman as well as the greater artist in general, the overall effect of the show is one of slight disappointment.

Given that, at various points in their careers, father and son shared drawing styles as well as subject matter — scenes of Venetian life, the commedia dell’arte, and so on — it is a curious thing that each of them, when most faithful to his own talents, approached the art of drawing in a manner diametrically opposed to the other’s. Indeed, it would not be an exaggeration to say that, between them, father and son represent the two conceptual halves of drawing’s empire.

For Giambattista (1696-1770), at his most typical and his best, drawing is the mercurial life force that spills out onto the page like a spray of uncorked champagne. Washes might account for shading and the occasional detail, but the quintessence of his art is ever and always an exuberation of lines, pure forms collecting into recognizable subject matter.

Surely there are moments in the Lehman show when Giandomenico (1727–1804) attempts the same thing. And to the untrained eye, he might appear to come close to his father. But in truth, his heart is not in it. His lines feel leaden, despite his calibratedstab at sprezzatura, or élan. The quicksilver agility of the father has vanished utterly. What defines Giandomenico’s drawings, rather, is a use of lines, usually shorter and more controlled than his father employed, to describe retinal realities until these lines coalesce into a comp.

In this regard, Giandomenico is a bizarre creature, a great draftsman who never drew a single decent line in his long career. That is to say that none of the lines is prepossessing in itself, as is usually the case with Giambattista. Taken together, however, they mass into a finished work of art that provides an invaluable record of Venetian life in the dying days of the republic. In truth, Giandomenico is a genre painter, a category that was and remained largely alien to Venetian art, but that began to seep into Northern Italy from Holland around the first half of the 18th century, especially in the works of men such as Giuseppe Maria Crespi.

Consider some of the depictions of Christ’s Passion on view at the Lehman. Surely these sunlit studies have got to be among the least passionate, least religious depictions of their chosen subjects even to be attempted by an Italian artist. In them, one finds that skewed and slightly scurrilous smirk, the nearly irreligious wink, that marks the son’s depictions of the commedia dell’arte, the endless brigades of hunchbacked Pulcinellas clumsily set into a somewhat unstable perspective.

It is curious that the drawings by the father that are included in the Lehman Collection consistently underplay the artist’s strength, so that he seems far closer in style to his son than he really is. There is really only one work, “One of the Hours Holding the Bridle of a Horse of the Sun,” that, in its dazzling draftsmanship, conveys the explosive brilliance of Giambattista at his best. More often, as in his “Seated Pulchinellos,” the artist charts a middle course that has something of the precision of the son, but also a leaven of abstractness and energy to the lines and the washes that suggests what Giambattista could do at his best. That level of artistry, however, is only rarely evident in the drawings now on view in the Lehman Collection.