Skip to main content

5 Carat Single Diamond Rings

to
61
1,579
184
1,165
583
492
480
254
231
129
99
65
64
62
48
36
27
25
23
22
21
20
7
7
6
2
2
1
1
1
60
46
31
12
11
Sort By
Art Deco 1.91 Carat Old European Cut Diamond Platinum Five Stone Band Ring
Located in Philadelphia, PA
Centering an old European cut diamond weighing approximately 1.13 carats total - G color with SI2
Category

Vintage 1930s Art Deco Band Rings

Materials

Diamond, Platinum

Mid Century GIA 1.58 1.30 Carats Old Mine Cut Diamonds Emerald Platinum Ring
Located in Beverly Hills, CA
One Mid Century GIA 1.58 1.30 Carats Old Mine Cut Diamonds Emerald Platinum Bypass Ring. Featuring
Category

Vintage 1950s Unknown Cocktail Rings

Materials

Diamond, Emerald, Platinum

Diamond Wedding Band Genuine Antique Deco Dated 4-24-49 Platinum Ring
Located in Dearborn, MI
Highlights 5 Matching Clean and Colorless Natural Antique Single-Cut Diamonds. Ensures 100% Authenticity as
Category

Vintage 1940s Art Deco Wedding Rings

Materials

Diamond, Platinum

Victorian Yellow Gold, Diamond, Ruby Navette Style Cocktail Ring
Located in Addison, TX
the size in the message section. Item Details: Ring Size: 5 3/4 Metal Type: Yellow Gold (If no
Category

Vintage 1920s Unknown Art Deco Fashion Rings

Materials

Diamond, Ruby, Yellow Gold

Art Deco Diamond 14 Karat White Gold Ivy Band Ring
Located in Philadelphia, PA
delicately with milgrain Motif is set with single cut diamonds weighing in total 0.20 carat - eye clean and
Category

Vintage 1930s Art Deco Band Rings

Materials

Diamond, White Diamond, Gold, 14k Gold, White Gold

Art Deco Diamond 18 Karat White Gold Engraved Band Ring
Located in Philadelphia, PA
Band ring is set to front by five single cut diamonds Weighing in total approximately 0.10 carat
Category

Vintage 1930s Art Deco Band Rings

Materials

Diamond, White Diamond, Gold, 18k Gold, White Gold

Art Deco Diamond Engagement Ring 900 Platinum Old Mine Cut Genuine .71 Carat
Located in Greensboro, NC
designer. The single cut diamond accents carry .10 carat total weight, SI1 - SI2 clarity, and H - I color
Category

Vintage 1920s Unknown Art Deco Engagement Rings

Materials

Diamond, Platinum

Art Deco Transitional Diamond 18 Karat White Gold Engagement Ring
Located in Philadelphia, PA
by single cut diamonds. Weighing in total approximately 0.05 carat - eye clean and bright. With a
Category

Vintage 1930s Art Deco Engagement Rings

Materials

Diamond, White Diamond, Gold, 18k Gold, White Gold

0.40ctw Diamond Ring Jacket Guard 14k Yellow Gold Size 6.5 Bridal
Located in McLeansville, NC
Gemstone Information: - Natural Diamonds - Total Carats - 0.40ctw Cut - Single Color - G - H
Category

21st Century and Contemporary Wedding Rings

Materials

Diamond, 14k Gold, Yellow Gold

J.E. Caldwell Art Deco Diamond Platinum Vintage Eternity Wedding Band Ring
Located in Philadelphia, PA
Featuring single cut diamonds channel set fully around Weighing approximately 0.42 carat total G/H
Category

Vintage 1930s Art Deco Wedding Rings

Materials

Diamond, Platinum

Beautiful Art Deco Platinum Aprox 1/2 Carat Center Diamond Filigree Shield Ring
Located in Addison, TX
Here we have an 1930's Art Deco Platinum aprox 1/2 cttw Old European Cut Diamond Shield Ring! The
Category

Vintage 1930s Unknown Art Deco Cocktail Rings

Materials

Diamond, Platinum

1920 s Art Deco 0.57 Carat Diamond 18 Karat White Gold Bombe Engagement Ring
Located in Philadelphia, PA
consistent with age Centering an old European cut diamond weighing 0.49 carat - G color with VS clarity Set
Category

Vintage 1920s Art Deco Engagement Rings

Materials

Diamond, White Diamond, Gold, 18k Gold, White Gold

Light Blue Natural Sapphire Diamond Ring
Located in Stamford, CT
ring pave set with small diamonds. Circa 1920 to 1930. Excellent condition. Looks great on the hand
Category

Early 20th Century Unknown Art Deco Engagement Rings

Materials

Diamond, Sapphire, Platinum

Art Deco GIA 4.80 Carat Blue Sapphire Diamond Platinum White Gold Cocktail Ring
Located in Beverly Hills, CA
: Thailand Treatment: No Heat Accent Stone: 18 Diamonds Cut: Single Weight: Approximately 0.55 Carats Color
Category

Vintage 1920s Art Deco Cluster Rings

Materials

Diamond, Sapphire, Gold, 18k Gold, White Gold, Platinum

Diamond Gold Star Ring
Located in Amsterdam, NL
A 14 carat white and yellow gold band ring set with 8 single cut diamonds (total circa 0.5 carats
Category

Vintage 1960s American Band Rings

Materials

White Diamond, 14k Gold

1960s Diamond Cocktail Ring
Located in Hicksville, NY
. Accent Diamonds, all round single cuts, weigh 1.50 carats total, ranging from G - I color, VS - SI
Category

Vintage 1960s Retro Cocktail Rings

Materials

Diamond, 18k Gold, Platinum

Vendome Retro 0.40 Carat Ruby Sapphire Emerald Diamond 18 Karat Gold Flower Ring
Located in Philadelphia, PA
Featuring a bouquet of flowers, centering 1 single cut diamond, 3 full cut emeralds, 4 full cut
Category

Mid-20th Century Unknown Retro Cocktail Rings

Materials

Diamond, Emerald, Ruby, Sapphire, 18k Gold

Art Deco 1.09 Carats Square Step Cut Sapphire Diamond 14 Karat White Gold Ring
Located in Philadelphia, PA
single cut diamonds. Weighing approximately 0.46 carat total. H/I color with VS1 clarity - bead set
Category

Vintage 1930s Art Deco Cocktail Rings

Materials

Diamond, White Diamond, Sapphire, Blue Sapphire, 14k Gold, White Gold

Natural Emerald Diamond Ring, 14k Yellow Gold, Ring, Emerald Diamond
Located in McLeansville, NC
piece. Stones: - diamonds, 5 stones - single cut round - 1.3 mm - approximately .04 total carats - G-H
Category

1990s Cluster Rings

Materials

Diamond, Emerald, 14k Gold, Yellow Gold

Vintage Diamond Navette Ring, 14K White Gold, Ring, Diamond Cluster
Located in McLeansville, NC
with prong set, round brilliant and single cut diamonds weighing approximately 1 total carat and with a
Category

Vintage 1970s Cluster Rings

Materials

Diamond, 14k Gold, White Gold

1925 Art Deco Diamond 18 Karat White Gold Orange Blossom Band Ring
Located in Philadelphia, PA
Band ring features seven old single cut diamonds Weighing in total approximately 0.21 carat with H
Category

Vintage 1920s Art Deco Band Rings

Materials

Diamond, White Diamond, 18k Gold, White Gold

Vintage Diamond Gold Ring
Located in Beverly Hills, CA
One Vintage Diamond Gold Ring. Featuring eight single cut diamonds with a total weight of
Category

Vintage 1970s Cocktail Rings

Materials

Diamond, Gold, 14k Gold

Retro French Diamond 18k Yellow Gold Ring
Located in Beverly Hills, CA
One Retro French Diamond 18k Yellow Gold Ring. Featuring 12 round brilliant and single cut diamonds
Category

Vintage 1940s Retro Engagement Rings

Materials

Diamond, White Diamond, Gold, 18k Gold, Yellow Gold

Vintage Snake Ring 18k Yellow Gold 5 Coils Sz 6 Band Serpent Jewelry
Located in Torrance, CA
small single cut diamonds total an estimated 0.02 carats. For centuries the snake has represented
Category

Late 20th Century Unknown Modern Band Rings

Materials

Diamond, White Diamond, Gold, 18k Gold, Yellow Gold

Old European Cut Round Diamond Platinum Ring
Located in Stamford, CT
.colorless 1 old European cut round diamond 1.82cts, D-E, SI1, 61.7 depth, 53% table 26 single cut diamonds
Category

Vintage 1910s Unknown Engagement Rings

Materials

Diamond, Platinum

Art Deco French 3.25 Carat Cushion Cut Diamond Onyx 18 Karat White Gold Ring
Located in Beverly Hills, CA
One Art Deco French 3.25 Carat Cushion Cut Diamond Onyx 18 Karat White Gold Ring. Featuring one
Category

Vintage 1920s French Art Deco Cocktail Rings

Materials

Diamond, Onyx, 18k Gold, White Gold

Mexican Opal 4.12 Carat Diamonds One of a Kind 18 Karat Yellow Gold Ring
By Mousson Atelier
Located in Bangkok, TH
Mexican Opal 4.12 Carat Diamonds One of a Kind 18 Karat Yellow Gold Ring Opals, unlike many other
Category

21st Century and Contemporary Thai Contemporary Cocktail Rings

Materials

Diamond, Opal, 18k Gold, Yellow Gold

Art Deco French GIA 2.25 Carat Old European Cut Platinum Ring
Located in Beverly Hills, CA
clarity. Accented by two single cut diamonds with a total weight of approximately 0.10 carat, graded I
Category

Vintage 1920s French Art Deco Engagement Rings

Materials

Diamond, Platinum

Vintage Colombian Emerald and Diamond Ring, GIA Certified.
Located in New York, NY
single cut : 1.05 carat Measurements : ring top: 3/4 by 3/4 inch Ring size : 5 1/2 Weight : 8.20 grams
Category

Vintage 1950s American Engagement Rings

Materials

Diamond, Emerald

Old Mine Diamond Art Deco Platinum Square Cocktail Ring
Located in Stamford, CT
Old mine diamond pierced square top ring in solid Platinum, circa 1920's 1 old mine cut diamond
Category

Vintage 1920s Cocktail Rings

Materials

Diamond, Platinum

Oval Cabochon Cut Turquoise and Diamond Ring 14 Karat Yellow Gold Halo .11 Carat
Located in Greensboro, NC
Diamonds Clarity: SI2 - I1 Color: G - H Cut: Single Total Carats: 0.11ctw Style: Solitaire with
Category

20th Century Chinese Solitaire Rings

Materials

Diamond, Turquoise, 14k Gold, Yellow Gold

1925 Art Deco Diamond 18 Karat White Gold Orange Blossom Band Ring
Located in Philadelphia, PA
Band ring features seven old single cut diamonds Weighing in total approximately 0.21 carat with H
Category

Vintage 1920s Art Deco Band Rings

Materials

Diamond, White Diamond, 18k Gold, White Gold

Art Deco Diamond Onyx 14 Karat White Gold Navette Dinner Ring
Located in Philadelphia, PA
Navette shaped dinner ring centers an old single cut diamond weighing approximately 0.03 carat
Category

Vintage 1920s Art Deco Cocktail Rings

Materials

Diamond, White Diamond, Onyx, Gold, 14k Gold, White Gold

Edwardian 1.37 Carats Round Brilliant Cut Diamond Platinum Tourbillion Swirl Rin
Located in Beverly Hills, CA
One Edwardian 1.37 Carats Round Brilliant Cut Diamond Platinum Tourbillion Swirl Ring. Featuring
Category

Vintage 1910s Edwardian Engagement Rings

Materials

Diamond, Brown Diamond, Platinum

Art Deco Platinum Diamond Ruby Engagement Ring .75ct
Located in Narberth, PA
shaped plaques, which are encrusted with bead-set single cut diamonds. The shoulders of the ring also
Category

Vintage 1920s Art Deco Engagement Rings

Materials

Diamond, Ruby, Platinum

1980s Blue Sapphire and Diamond 14 karat Yellow Gold Low Profile Fashion Ring
Located in Towson, MD
crisscross design, exuding elegance and sophistication. The ring features approximately 0.48 carats total
Category

Vintage 1980s Fashion Rings

Materials

Diamond, Sapphire, 14k Gold, Yellow Gold

Retro Diamond 14K Yellow Gold Platinum Cocktail Ring
Located in Beverly Hills, CA
karat yellow gold with diamonds set in platinum with purity marks. Circa 1940. The ring is a size 5 and
Category

Vintage 1940s Retro Cocktail Rings

Materials

Diamond, White Diamond, Gold, 14k Gold, Yellow Gold, Platinum

Platinum Lapis Diamond Ruby Ring
Located in Houston, TX
rubies. The Lapis weighs 22.0 carats. There are eighteen (18) single cut diamonds totaling 0.15 carats
Category

Vintage 1930s Unknown Cocktail Rings

Materials

Diamond, Lapis Lazuli, Ruby, Platinum

Art Deco Diamond 18 Karat White Gold Orange Blossom Wedding Band Ring
By Orange Blossom
Located in Philadelphia, PA
Featuring a row of single cut diamonds channel set east to west Weighing approximately 0.14 carat
Category

Vintage 1930s Art Deco Engagement Rings

Materials

Diamond, Gold, 18k Gold, White Gold

Oakes Arts Crafts Diamond 14 Karat Yellow Gold Antique Floral Band Ring
Located in Philadelphia, PA
foliate and petal details Featuring single cut diamonds flush set around Weighing approximately 0.18
Category

Vintage 1920s Art Nouveau Band Rings

Materials

Diamond, Gold, 14k Gold, Yellow Gold

10W Gold, Opal Diamond Ring
Located in McLeansville, NC
approximately .22 carat surrounded by single cut round diamonds weighing approximately .05 total carats and with
Category

1990s Cluster Rings

Materials

Diamond, Opal, Gold, 10k Gold, White Gold

Diamond Encrusted Platinum Dome Ring
Located in Scottsdale, AZ
VS1 single cut natural 0.042 & 0.012ct Diamonds (total carat weight estimated at 1.19ct). Total ring
Category

Vintage 1960s Unknown Dome Rings

Materials

Diamond, Platinum

Art Deco .63ctw Diamond Engagement Ring, Platinum, Ring Size 7
Located in McLeansville, NC
Stones: diamond old european cut, 1 5 mm approximately .50 total carats GH color/ I1 clarity *w
Category

Vintage 1910s Art Deco Engagement Rings

Materials

Diamond, Platinum

Opal Diamond Navette Ring, 14KT Yellow Gold, Ring
Located in McLeansville, NC
halo of single cut round diamonds weighing approximately .06 total carats and with a tapered band
Category

Vintage 1970s Fashion Rings

Materials

Diamond, Opal, 14k Gold, Yellow Gold

Cushion Cut GIA Certified Diamond Halo Engagement Ring
By Roman Malakov
Located in New York, NY
Cushion cut diamond center stone weighing 0.79 carats that GIA certified as G color and VVS2
Category

21st Century and Contemporary American Engagement Rings

Materials

Diamond, 18k Gold, White Gold

Rose Gold Diamond Wave Ring
Located in Coral Gables, FL
14 Karat Rose Gold Diamond Swirl Ring Featuring 160 Single Cut Diamonds Of SI Clarity & H Color
Category

21st Century and Contemporary Dome Rings

Materials

Diamond, 14k Gold, Rose Gold, White Gold

Past Era Art Deco Aquamarine Diamond Gold Cocktail Ring
Located in Houston, TX
(total carat weight: 6.48 carats) and four Old European-cut and two single-cut diamonds (total carat
Category

Vintage 1920s Unknown Art Deco Cocktail Rings

Materials

Aquamarine, Diamond, 14k Gold

1920s Platinum Diamond Engagement Ring
Located in Chicago, IL
Wonderful Vintage 1920s Engagement Ring, Platinum and centrally set with a 1.10 Carat old European
Category

20th Century American Edwardian Engagement Rings

Materials

Diamond, Sapphire, Platinum

Platinum Tourmaline Diamond Halo Ring - Cushion 5.37ctw Paraiba Type
Located in Greensboro, NC
Diamonds Carat(s): .48ctw Cut: Single Color: G - H Clarity: VS1 - SI1 Total Carats: 5.37ctw Style
Category

21st Century and Contemporary Cocktail Rings

Materials

Diamond, Tourmaline, Platinum

Unique 18kt Floral Diamond Ring
Located in San Francisco, CA
shaped diamonds fashioned as petals with a single fine round diamond at the center of the floral design
Category

21st Century and Contemporary Unknown Fashion Rings

Materials

Diamond, 18k Gold, White Gold

Mid Century Diamond Platinum Flower Eternity Band
Located in Beverly Hills, CA
about timeless charm. This ring boasts 16 dazzling single cut diamonds, with a total weight of
Category

Vintage 1960s Wedding Rings

Materials

Diamond, White Diamond, Platinum

Ruby Diamond Band Ring, 9K Yellow Gold, Ring, Stackable
Located in McLeansville, NC
alternating round cut rubies weighing approximately .20 total carats with single cut round diamonds weighing
Category

Vintage 1970s Band Rings

Materials

Diamond, Ruby, 9k Gold, Yellow Gold

Heart Shaped Sapphire Diamond Engagement Ring
Located in Chicago, IL
blue sapphire framed by 21 single cut diamonds. The sapphire is approximately 5 carats. Estimated
Category

Vintage 1930s Engagement Rings

Materials

Diamond, Blue Sapphire

Original Diamond and Ruby Leaf Ring
Located in Miami, FL
carat and an old European cut diamond with an estimated weight of .75ct a row of 5 single cut diamonds
Category

20th Century American More Rings

Materials

Diamond, Ruby, White Diamond, 14k Gold, Yellow Gold

GIA Certified 1.54 Carat Orange Red Cushion Spinel Platinum Gold Engagement Ring
Located in Stamford, CT
heat. GIA certificate # 1152137500. 6 single cut diamonds, approx. total weight .06cts, H, VS2 Size 5
Category

Early 20th Century Engagement Rings

Materials

Diamond, Spinel, 18k Gold, White Gold, Platinum

Art Deco Platinum Band with 11 Single Cut Diamonds Along the Top Stackable Band
Located in Addison, TX
shimmering diamonds are 0.055 total carats of classic beauty. What a wonderful band to pair with your
Category

Vintage 1930s Unknown Art Deco Bridal Rings

Materials

Diamond, Platinum

Rectangle Lapis Diamond Two-Tone Gold Cocktail Ring
Located in Stamford, CT
18k yellow gold lapis and diamond ring. Rectangular lapis is decoratively covered by wavy bands of
Category

Mid-20th Century Cocktail Rings

Materials

Diamond, Lapis Lazuli, Gold, 18k Gold, White Gold, Yellow Gold

  • 1
  • ...
Get Updated with New Arrivals
Save "5 Carat Single Diamond Rings", and we’ll notify you when there are new listings in this category.

5 Carat Single Diamond Rings For Sale on 1stDibs

Find an expansive variety of 5 carat single diamond rings available on 1stDibs. These distinct designs — crafted with great care and often made from Gold, Yellow Gold and 14k Gold — can elevate any look. Find a collection of 161 vintage versions or 491 modern creations for a more contemporary example of these cherished accessories. Our collection, which features older pieces for sale from the 19th Century and newer versions made as recently as the 21st Century, has proven very popular over the years. There are many different pieces in our collection of 5 carat single diamond rings to choose from, but Art Deco and Contemporary 5 carat single diamond rings are of considerable interest. There have been many well-made iterations of these items over the years, but those made by Single Stone, NYF Jewellery and Meghna Jewels are often thought to be among the most beautiful. Today, if you’re looking for old european cut 5 carat single diamond rings and are unable to find the perfect match, our selection also includes single cut and emerald cut alternatives. When shopping our range of 5 carat single diamond rings, you’ll find that there are less available pieces for men today than there are for women.

How Much are 5 Carat Single Diamond Rings?

Prices for 5 carat single diamond rings can differ depending upon size, time period and other attributes — at 1stDibs, these accessories begin at $350 and can go as high as $119,894, while 5 carat single diamond rings, on average, fetch $12,143.

The Legacy of Diamond in Jewelry Design

Antique diamond rings, diamond tiaras and dazzling vintage diamond earrings are on the wish lists of every lover of fine jewelry. And diamonds and diamond jewelry are primarily associated with storybook engagements and red-carpet grand entrances — indeed, this ultra-cherished gemstone has a dramatic history on its hands.

From “A Diamond Is Forever” to “Diamonds Are a Girl’s Best Friend,” pop culture has ingrained in our minds that diamonds are the most desired, the most lasting and the most valuable gemstone. But what makes the diamond so special? Each stone — whether it’s rubies, sapphires or another stone — is unique and important in its own right. April babies might claim diamonds for themselves, but just about everyone wants this kind of sparkle in their lives!

There are several factors that set diamonds apart from other stones, and these points are important to our gem education.

Diamonds are minerals. They are made up of almost entirely of carbon (carbon comprises 99.95 percent; the remainder consists of various trace elements). Diamonds are the hardest gemstones, ranking number 10 on the Mohs Hardness Scale. Even its name, diamond, is rooted in the Greek adamas, or unconquerable. The only object that can scratch a diamond is another diamond. Diamonds are formed deep within the earth at very high temperatures (1,652–2,372 degrees Fahrenheit at depths between 90 and 120 miles beneath the earth’s surface) and are carried up by volcanic activity. Diamonds are quite rare, according to the Gemological Institute of America, and only 30 percent of all the diamonds mined in the world are gem quality.

In the 1950s, the Gemological Institute of America developed the 4Cs grading system to classify diamonds: clarity, color, cut and carat weight. Not all diamonds are created equal (there are diamonds, and then there are diamonds). The value of the diamond depends on the clarity (flawless diamonds are very rare but a diamond's value decreases if there are many blemishes or inclusions), color (the less color the higher the grade), cut (how the diamond’s facets catch the light, certain cuts of diamonds show off the stone better than others) and carat weight (the bigger, the better).

When you start shopping for a diamond engagement ring, always prioritize the cut, which plays the largest role in the diamond's beauty (taking the time to clean your diamond ring at least every six months or so plays a role in maintaining said beauty). And on 1stDibs, a range of buying guides can be found for those in the market for antique engagement ringsvintage engagement rings or Art Deco engagement rings

Shop antique and vintage diamond rings, diamond necklaces and other extraordinary diamond jewelry on 1stDibs.  

Finding the Right Rings for You

Antique and vintage rings have long held a special place in the hearts of fine jewelry lovers all over the world.

No matter their origin or specific characteristics, rings are timeless, versatile accessories. They’ve carried deep meaning since at least the Middle Ages, when diamond rings symbolized strength and other kinds of rings were worn to signify romantic feelings or to denote an affiliation with a religious order. Rings have also forever been emblematic of eternity.

Over time, rings have frequently taken the form of serpents, which have long been associated with eternal life, health and renewal. Italian luxury jewelry house Bulgari has become famous for its widely loved Serpenti motif, for example, and its Serpenti ring, like the other accessories in the collection, began as an homage to jewelry of the Roman and Hellenistic eras. The serpent is now a popular motif in fine jewelry. Jewelry devotees have long pined for rings adorned with reptiles, thanks to antique Victorian rings — well, specifically, Queen Victoria’s illustrious engagement ring, which took the form of a gold snake set with rubies, diamonds and an emerald (her birthstone). Designs for Victorian-era engagement rings often featured repoussé work and chasing, in which patterns are hammered into the metal.

Engagement rings, which are reliably intimidating to shop for, are still widely recognized as symbols of love and commitment. On 1stDibs, a range of buying guides can be found for those in the market for antique engagement ringsvintage engagement rings or Art Deco engagement rings

The most collectible antique engagement rings and vintage engagement rings are those from the Victorian, Edwardian and Art Deco eras. Named for the monarchies of the four King Georges, who in succession ruled England starting in 1714 (plus King William’s reign), antique Georgian rings, be they engagement rings or otherwise, are also coveted by collectors. Pearls, along with colored gemstones like garnets, rubies and sapphires, were widely used in Georgian jewelry. The late-1700s paste jewelry was a predecessor to what we now call fashion or costume jewelry

The Art Nouveau movement (1880–1910) brought with it rings inspired by the natural world. Antique Art Nouveau rings might feature depictions of winged insects and fauna as well as women, who were simultaneously eroticized and romanticized, frequently with long flowing hair. Art Deco jewelry, on the other hand, which originated during the 1920s and ’30s, is by and large “white jewelry.” White metals, primarily platinum, were favored over yellow gold in the design of antique Art Deco rings and other accessories as well as geometric motifs, with women drawn to the era’s dazzling cocktail rings in particular.

Whether you’re hunting down a chunky classic for a Prohibition-themed cocktail party or seeking a clean contemporary design to complement your casual ensemble, find an exquisite collection of antique, new and vintage rings on 1stDibs.