FASHION CURRICULUM : Be Blue to Your School : In their latest incarnation, loyal and versatile denim jeans turn back to the deep hues and natural fit of the ‘50s.

It’s been scrubbed with everything from pebbles to golf balls. It’s been bleached, and it’s been dyed. It’s been stretched, shrunken and shredded with razors. No matter what form it takes, denim never fades.

Every fall, denim returns as the uniform of choice for kids headed back to school.

In the ‘50s, they liked their denim dark and crisp; natural- fitting blue jeans with rolled cuffs were the rage. Marilyn and James Dean wore them.

In the ‘60s, love children expressed themselves by decorating their denim with embroidered slogans and peace patches. Denim bell-bottoms and hip-huggers were hot in the ‘70s, followed

by the skin-tight, top-stitched and label-conscious designer jeans of the ‘80s.

Thus far, the ‘90s has seen oversized and faded denim, but the fashion pendulum is moving away from huge jeans. In its latest incarnation, denim has turned back to the deep blue hues and natural fit of the ‘50s.

“We don’t even [stone] wash them. The jeans come out very stiff, like in the ‘50s, and you wear them with the big bucket cuffs,” says Mossimo Giannulli, founder of Mossimo Inc. in Irvine.

“The darker washes are really important,” he says. “They bring out the characteristics of the denim and make it interesting.”

Giannulli’s new denim line features Slim Jims--jeans made of deep indigo denim with narrower silhouettes.

“Denim becomes very smart, very modern,” he says. “It’s a mod London thing.”

Like Mossimo, Quiksilver’s Q.S.D. (Quiksilver Saltwater Denim) line is also making leaner jeans.

“It’s the old Marilyn Monroe jeans--they’re almost crisp-looking,” says Melissa Martinez, designer for Q.S.D. in Costa Mesa. “The big baggy look is way over.”

To work with denim--which is naturally neutral-colored--Martinez has to be part chemist. She experiments with different dyes and washes, from a “volcanic wash” that thrashes the denim enough to leave holes to a gentle “ocean-wash finish” that simply softens the material.

“Wash houses [where denim is dyed] use everything from fake rocks to golf balls to wash the denim,” she says. “The majority of people still like jeans that look lived in.”

Q.S.D.’s latest denim development is called Plastic Fantastic, a collection of denim made from recycled plastic bottles.

“Two big soda bottles go into every pair of jeans,” Martinez says. The plastic is shredded and melted, then twisted into fibers and woven into the cotton. It looks beautiful, and the hand [feel of the fabric] is great.”

Q.S.D. has also developed new techniques for tinting denim to make it look aged.

“We’re experimenting with the dyes to give the denim a reddish, greenish or yellowish tint. It has a retro feel,” Martinez says.

B. C. Ethics has designed a line of rock-a-billy jeans that it calls “Clean, Dirty and Filthy.”

“They look like you’ve been under a car,” says Tim Anderson, owner of Nothing Shocking, an alternative clothing store in Fullerton.

“They feel as if they have grease on them, but they’re clean. It’s like they soaked them in oil, then washed and washed and washed them,” he says. The greasy jeans sell for about $60.

Some kids like wearing the fitted ‘50s-style jeans with biker boots.

“They’re rolling them up with the boots like Harley riders wear,” Anderson says.

Back-to-school kids have to decide what jeans to buy and the cool way to wear them.

Lots of kids like layering their denim, putting a button-down denim shirt over a T-shirt and jeans, says Mike Schillmoeller, co-owner of Counter Culture, a sportswear manufacturer in Huntington Beach.

They want their jeans long and loose.

“The kids like to cut off the legs of the jeans. It’s kind of edgy,” Schillmoeller says.

Counter Culture’s fall line features indigo denim and sanded and brushed bull denim dyed in earthy shades of tan, pale olive, gray and steel blue. The button-up overshirts, shorts and jeans (about $40 to $58) are carried at Beach Access in South Coast Plaza, the Brea Mall and Huntington Surf & Sport.

The key to denim’s longevity, say designers and manufacturers, is its versatility, comfort and durability.

“The fabric is as strong as it gets. You can wear it for years,” Schillmoeller says.

The long-lasting, universal appeal of denim also has to do with image.

“There’s always a rebellion about it, a James Dean attitude,” Giannulli says. “It’s a staple. It’s been around so long now, it will never go away.”