Her friends have kidded her that she’s frozen in time.

Dora Timmerman Bayer has lived in the same east Wichita house since it was built in 1958. Her home, in the mid-century modern style, is a time capsule, in the Pine Valley Estates neighborhood near 13th and Woodlawn. Hanging from the home’s entryway is a Space Age-inspired Sputnik lamp, with a starburst design. In today’s market for authentic 1950s and 1960s home furnishings, the lamp is a hot item. A similar one is listed at $595 on eBay. The fixture fits with the home’s angular, linear architecture, with vaulted ceilings and unpainted wood beams. Stacked limestone covers a living room wall. A three-part pendant lamp, each piece shaped like a bowling pin, hangs over the dining room table, just as it has hung since Eisenhower was president.

Wichita has a wealth of houses built in the 1950s and early to mid-1960s. But every year, house by house and piece by piece, more of the distinctive interior features are disappearing as owners update, sometimes without appreciation for the valuable things they are tearing out, covering up or irreversibly altering.

In the process, pieces of the city’s history are disappearing, preservationists say. “Absolutely, they are” historically significant, said Kathy Morgan, senior planner in the city’s Historic Preservation Office.

Those pieces of history are lost because too often people don’t recognize that something from the mid-century, even a small one-story ranch home, has historic value.

The 1950s and early 1960s houses were the starter homes of World War II and Korean War veterans and the dream homes of established families. They reflected a general optimism, the bounty of mass production, a fascination with outer space and an expression of modern architecture attempting to blend the inside of the home with the outside through picture windows, sliding glass doors and backyard patios.

Inside, skilled carpenters did custom work, and stone and brick masons built fireplace walls that would be expensive to replicate now, with materials that in some cases are no longer available or are cost prohibitive.

Two of the city’s mid-century ranch-style homes are listed on the National Register of Historic Places, but many more could merit the designation, Morgan said. She estimated that the city might have 20,000 homes built in the mid-century, in neighborhoods including Benjamin Hills, Bonnie Brae, Crestview Lakes, Forest Hills, Indian Hills, Pine Valley Estates, Rockwood, Spring Acres, The Village and Woodlawn Village.

The mid-century houses came in different styles and reflect different historical eras, Morgan said. They show Swiss, Asian and agricultural influences, and sometimes a mix of those in the same house. One of the two homes on the national register, in Woodlawn Village, near Central and Woodlawn, was designed by the well-known architect William Caton. Inside and outside, the house looks like an English cottage, with lots of exposed red brick and darker wood.

“There are a lot of people out there that are quietly taking care of their mid-century homes,” Morgan said.

People can maintain, renovate and put their own stamp on a mid-century home without removing the features that help it retain its place in history. Flooring can be replaced or refinished, walls can be repainted, and appliances and other mechanical items can be switched out for safety, practicality and energy efficiency.

Whatever people do, they shouldn’t throw things away, Morgan said. Someone values it. People might be surprised how much money a vintage built-in stove or oven might fetch from people who like the retro look or the quality. A neighbor or friend might covet the original wood trim, multi-paned front door or kitchen hardware someone is tossing. The ribbed plastic light switch covers that someone might throw in the trash are being offered on eBay for $3 to $10 each.

The push to keep up with the latest trends is why a lot of original interiors are continuing to disappear, said Barbara Anderson, associate professor and head of the Department of Apparel, Textiles and Interior Design in the College of Human Ecology at Kansas State University. Anderson considers herself a preservationist.

Before someone takes a 1958 house and tries to make it look like 2013 inside, they should consider leaving it as it was intended, “true to the original aesthetic,” Anderson said.

The drive to keep up with fashion is why a lot of original woodwork has been painted over. Today’s interior designer might tell TV viewers to paint the wood trim and fireplace brick a stark white, when the 1957 designer thought it should remain with the natural-wood look or the bare red-brick finish. Once the wood or brick gets painted, it’s time-consuming and costly to reverse.

Modern-style architects who designed the mid-century houses thought “materials should be true to themselves,” Anderson said. “A material was a material, and you left it as it was … so they rarely painted wood,” unless it was on the outside of the house, and then only to protect it. Indoors, stain and varnish was applied only to protect the material or enhance the natural qualities, like the grain pattern in a piece of wood.

By the 1970s and 1980s, some of the original owners gutted their vintage-modern kitchens, replacing lighter wood cabinets with oak versions that were the new fashion. Original tile countertops in 1950s colors such as green and tan gave way to muted laminate. In the 1990s and 2000s, some of the original wood and tile got replaced with granite and the Tuscan style popularized in TV home improvement shows and advertising. Original cabinets sometimes ended up being hung for storage in the garage, said Jay Price, associate professor and director of the public history program at Wichita State University. Price owns a 1954 house that retains some of its original interior, including a room divider with 5-foot-tall glass rods.

Price, 43, said he hated the 1950s look when he was teenager, but later he began to look at it differently, as something playful.

Mid-century bathrooms got gutted partly because someone didn’t like the mint-green or pink tile, made popular in the ’50s partly because pink was the favorite color of Mamie Eisenhower, the first lady from 1953 to 1961. In the eyes of a mid-century fan, taking away the vintage color is stripping away the character. There has been a pro-pink backlash, including websites such as savethepinkbathrooms.com.

Nobody laid tile to last better than the mid-century craftsmen, said Anderson, the K-State professor. Up until about 1970, the tile layers set the pieces in a thick “setting bed” of mortar, about an inch and a half deep. But now it’s set in only about a quarter inch. “I think it was simply because it was cheaper and faster,” she said. The old tile “doesn’t crack like today’s tile.”

One of the two Wichita mid-century homes on the National Historic Register, the distinctive McLean family home in the Benjamin Hills neighborhood off West 21st Street, still bears its original tile bathrooms, in varying combinations of pink, blue and green.

Angela Addario-McLean grew up in the home, completed in 1956. “It would have never occurred to me to change it,” she said. Light green and black tiles still cover the kitchen counter, beneath cabinets with ribbed glass doors.

The rooms retain their honey-brown wood trim. Addario-McLean said her grandmother, who had the home built, liked the natural look of the wood.

The house, owned by Addario-McLean’s mother, Julianne McLean, is known for its exterior walls of earth-tone pink and white marble from Georgia. A massive wall of sparkly white marble stones runs through the interior.

Around the corner from the McLean house sits a 1957 mid-century modern owned by Carter and Lori McEvoy. He bought the home about 10 years ago to furnish it with his extensive collection of mid-century modern furnishings. It took McEvoy nearly 20 years to find the right home. When he stepped onto the flagstone inside and saw the soaring windows and all the light-colored Honduran mahogany, jutting at different angles, layered in different planes, he knew he had found his time capsule. The kitchen has a fold-down Frigidaire cook-top stove. The wet bar has a liquor dispenser. His Rio red-accented 1958 Corvette looks like it belongs with the house. Friends call it the “Jetson house.”

The staircase to the second floor is a work of art, with intersecting glass panels embedded with leaf designs and lattice work.

When he was trying to buy the house, he heard from real estate agents that prospective buyers were talking of tearing out a section of the galley kitchen to enlarge it. That would have been McEvoy’s nightmare. Enlarging the kitchen would have meant taking out the funky cooktop, an original countertop and a copper-colored clock set into a wooden beam.

“I’d like to see all these homes protected,” McEvoy said.

To him, the house represents “just an exciting time … when anything was possible.”

In houses like McEvoy’s and Timmerman-Bayer’s, you can go back in time with something that still works today.

In the hallway bathroom at Timmerman-Bayer’s house in Pine Valley Estates, you step onto rectangular floor tiles, still shiny and tight, walk past honey-colored wood cabinets with brilliant metal handles, work faucet knobs that look like dark green billiard balls set in chrome. The wallpaper remains vibrant, with a blue-and-green circle pattern. A friend with an artistic eye photographed the wallpaper.

If the Smithsonian wanted an exhibit showing a 1950s American bathroom, this is it.