ART : Museums’ Misunderstood Works : When catalogues are good, they can be explanatory, insightful and historical.

You just saw the exhibit, and now you pop into the bookshop--to pick up a post card of a favorite work of art, maybe, or to browse the magazines or ogle the jewelry. But have you considered buying the exhibit catalogue?

Poor things, those exhibition catalogues are possibly the most misunderstood and overlooked items museum bookstores stock. To be sure, many are not particularly easy to read. Some don’t have good illustrations. And the ones that aren’t printed in soft-bound editions tend to be on the pricey side.

Yet catalogues are perhaps the most important product a museum has to offer. Years after a show has come and gone, the catalogue remains to testify to its existence and to the reasons it was created in the first place.

One major role of art museums is to interpret art--to explain what it says about the person or culture that made it, to help us appreciate what’s there and understand what isn’t. This is the sort of information that’s too bulky and distracting to pack into a label on the wall, too complex to be scanned by a footsore viewer.

So catalogues are where a museum gets to rack up points for scholarship. The curator explains the train of thought that led to selecting particular pieces for the show. Essays reinterpret works of art in light of newly discovered information, new theories are proposed, and long-held beliefs about the art in question are held up to the light to see if they still make sense.

And there’s more. A good catalogue for a historical show will include relevant essays on the period as a whole. (What was the political situation? How was the economy doing? What was playing at the theater? What kind of furniture did people have?)

A substantial catalogue about the work of a particular artist will include a biographical essay that traces the points at which everyday life and the making of art intersected. (Was it easier to work once she moved to the country? Did he keep painting his ex-wife’s face after the divorce?)

You find out what works of art the artist saw, which other artists he knew and how they mayhave influenced--or hindered--his work. Although these influential works probably aren’t includedin the exhibit itself--because they’re scattered in collections all over the world, or have been lost or destroyed--they are apt to be illustrated in the catalogue.

In this frantic age, when there are never enough hours in the day to do it all, catalogues also serve as substitutes for shows you never got to see, whether they opened 3,000 miles away or in your own city. Although you’ve missed the visceral experience of standing in front of the actual work, you do get an idea of what it looks like, along with useful information you can browse at your leisure.

Living artists benefit from catalogues for obvious reasons: Their work is fussed over in print and immortalized in photographs. Collectors not only become aware of the breadth of the artist’s work--they also are likely to be impressed by seeing it between two covers. (“If the X museum went to the trouble to put out a book about it, this work must be good.”)

Collectors who already own work by the artist stand to gain by having the piece reproduced in a museum catalogue. Again, the piece gains prestige by being singled out by the museum, which is likely to be translated into a more advantageous price if the collector chooses to sell.

One potentially smarmy side effect, however, is that collectors sometimes offer to pay for catalogue reproductions of works of art they own. The museum gets the expensive color plate it might not have been able to afford, the argument goes, and the collector can add a notch to his belt by having the work published under the museum’s aegis. The problem is that the particular work may not be of top quality, and the odor of payoff subverts the tradition of disinterested scholarship. If a collector pays for a reproduction, can an essayist still feel free to criticize the work or demote it to a lower rank in the artist’s oeuvre ?

Other problems with catalogues are much more clear-cut and involve no moral dilemmas, only failures of nerve, resources or energy.

Catalogues about a single artist sometimes sink to the level of panegyric. Everything this person did was great, according to the slobbering essayist. He or she would have you believe that the artist single-handedly maintained the level of art of his time, never had a bad day (much less a bad decade), and continues to produce brilliant work--even if, in fact, he’s really doing tired knock-offs of the stuff that initially made him famous.

And then there are shows that don’t have catalogues at all. “We have no money!” cry the sponsoring institutions. But not every catalogue has to be a flashy number printed on expensive coated stock and crammed with color photos.

Particularly at college and university galleries, the most important goal is to introduce the work in a meaningful way. A stapled handout run off on a copy machine can be a useful tool, anticipating the curious student’s questions and instilling the idea that art is just as rich and complex a subject as history or psychology. These days, when too many people have come to equate art with fancy price tags, even the humblest catalogue has yeoman work to do.