Harry Bertoia (1915-1978) moved to Pennsylvania from California to work for Knoll in 1950. Knoll is the manufacturer and copyright holder of all Bertoia chairs. Chairs, based on steel grid wire forms, were designed by Harry Bertoia between 1950 and 1951 and further developed for production by Harry and the development team consisting of Richard Schultz, Don Pettit and Bob Savage in 1951 – 1952. They were first introduced in December 1952, and have enjoyed steady continuous production since 1953. To state the obvious, nearly all products that have been in production for over 63 years undergo evolutionary changes over time.  Most are a response to field failures, structural improvement or cost reduction.  Others are a response to external forces.

For the sake of discussion, one can consider all Knoll Bertoia chairs as being either early style (1986 and earlier) or late style (1986 and later).  Prior to 1986, all Bertoia chairs were manufactured in East Greenville, Pennsylvania, or overseas by Knoll subsidiaries or under license.  At various times, Bertoia chairs were manufactured in Argentina, Belgium, Finland, France, Germany, Italy, Japan, Sweden and Switzerland.  All chairs of pre-’86 manufacture are very similar and are often only distinguishable by the wire diameters used (close metric diameter equivalent to US standard wire gauges.) See Photo 1 with yellow tags. It must be noted that, since foreign-made Bertoia chairs were never imported to the US, that it is very unlikely to encounter them here in the US.

All chairs made before 1986 are characterized by lightness and transparency.  Harry liked to think of his chairs as being “mainly made of air.”  That changed when the manufacture of the entire Bertoia line was shifted to Italy. At that time, the collection was retooled and major changes were made. Most obvious was the significant increase in wire diameter used throughout which changed the character of the chairs from transparency to form. See Photo 2.

PHOTO 1: Note the balanced corner radius as well as the thin wire diameter (“mainly made of air”) on this early style side chair. Compare this with the thicker wire diameter of the chair in the next image.

PHOTO 2: Note the thicker wire diameters of the 1986+ Italian made chairs of the late style, and the horizontal nature of the upper corner cells. Compare the light and transparent early chair with the thicker-wired form chair post 1986. All authentic Knoll Bertoia chairs have the single rim wire.

Other changes include altering the seat-back angle, the addition of a “waterfall” at the front edge and the use of the “paperclip-type” base connectors.

Many other minor changes have taken place over the years.  Most of the comments below are specific to the 420 Side Chair but apply to other models as well. These include:

  • GLIDES – Various glides have been used over the years… or no glides at all.  The first ones were extrusions that snapped on (and unfortunately snapped off).  Later ones are injection-molded with an integral pin that is driven into a blind hole on the bottom of the base.
  • “KNOLL” STAMP – In 2004, Knoll began to discreetly stamp the word “Knoll” on the upper part of the base.
  • UPHOLSTERY – All chairs are available with or without upholstery, either in the form of a seat pad or fully upholstered.
  • LINE ADDITIONS – During the 1950s and 60s, a number of additions were made to the original scope.  These included the 427 fiberglass version of the 420 shell, the 425 (child-size 420 chair), the 426 (baby-size version of the 425, and the 428 barstool (in two heights).  During the 2000s, two more designs were added.  The Asymmetric Chaise, which was part of the original scope but never produced, was finally put into production in 2005. In addition, a new scaled-down child’s version of the 421 small diamond chair (never part of the original scope) was also introduced.  Finally, an injection-molded polypropylene version of the long discontinued 427 shell (side chair) was reintroduced in 2016.

Tips for recognizing authentic Knoll chairs

Despite the evolutionary and more revolutionary changes (newer Italian production) that have taken place over the years, it’s surprisingly easy to spot the originals.  While the comments below are specific to the 420 side chair, they generally apply to the others as well.  We look at two places which 99% of the time positively identify genuine Knoll chairs from the knock-offs.

First is the upper back.  On the Knoll chairs, the top basket wire is a fair curve that mimics the curvature of the top of rim wire.  The top corners are perhaps the most critical clue.  The corner radius is neither too “soft” nor too “tight” (compare to above photos of Knoll chairs for a reference).  Also, the “cell” described by the basket wires (both horizontal and vertical) and the rim wire at the top corner is horizontal in character (very unlike nearly all knock-offs).

Second is the base.  The inside bend radius is very tight on all Knoll chairs.  A 1/2” diameter dowel should nest neatly on the inside of any base bend (knock-offs have a much more generous bend radius.)

Another detail on the Knoll chairs is that the grid wires are cut at an angle (some knock-offs have a straight blunt cut of the grid wires). See Photo 3.

PHOTO 3: The “paperclip type” base connector, angle-cut grid wires, and the front rim wire on top of grid wires in a “waterfall” identify an authentic Knoll Bertoia chair.

Tips for identifying a knock-off

It’s truly amazing that any company choosing to knock off an iconic product such as the Bertoia collection should be so sloppy in detail and make so many changes that scream knockoff!  But such is the case.

Descriptive words such as “Bertoia style,” “in the manner of Bertoia,” “inspired by Bertoia,” or “Bertoia reproduction” are a sure tip-off that it’s a copy. If the word “Knoll” is mentioned, it is still no guarantee as to its authenticity.

Many manufacturers of knock-offs utilize a “double rim-wire.”  While the double rim-wire was used for small number of 420 production chairs in early 1953, they were quickly replaced with a single larger diameter rim-wire.  Very few double rim chairs were shipped to customers.  Note that a double wire rim has always been used on the ottoman and asymmetric lounge and a partial double-rim has always been used on the 423 “Bird chair.”  Every new double-rim side chair is a knock-off.

PHOTO 4: An early double rim wire
original, rarely found today.

PHOTO 5: From left: 1953 double edge wire, 1953 double edge two tone thick plastic with original seat pad, early black thin wire, another early black thin wire with wide
clip connectors, white with short leg extensions, post 1986 with front edge waterfall and thicker wire – all authentic Bertoia side chairs.

The top corner tells a lot.  Most knock-off side chairs have “soft shoulders”; a much larger corner radius that lacks definition.  The top corner cell is nearly always more square or vertical than horizontal (as it should be).  Also, the top (horizontal) basket wire is often visually clumsy compared with the Knoll version. See Photo 5.

Finally, the base.  All knock-offs have a much larger bend radius than the authentic Knoll versions.  It must be noted that all pre-1986 chair bases consist of two pieces (upper and lower) and are resistance welded in an overlap condition.  Most knock-offs are “butt welded” with no overlap.  It must be noted that some Italian made Knoll chairs are made in a similar way but the welds are much neater.

It’s quite instructive to simply Google “Bertoia furniture knock-offs” and compare with pics of the real Knoll chairs.

PHOTO 6:  Modern double rim wire plus no base/leg
overlap and an overly generous corner radius;
all sure signs of a current knock off.

A few other notes

chair_article_photo_9_compactEames vs. Bertoia There seems to be some confusion on the Eames wire chair vs. the Bertoia wire chairs. Harry Bertoia worked with Charles Eames in the late 1940’s and was toying with, and making drawings of, the wire grid concepts. Eames carried this idea to fruition. Below is the Eames wire chair first produced by Herman Miller in 1950. The Bertoia chairs have a similar same wire grid concept but came out in 1952.

PHOTO 7: Eames wire chair, not to be confused with the Bertoia wire chairs (photo courtesy Herman Miller)

Why is authenticity important? Why is it important to get an authentic designer chair? Why not get a reproduction that looks roughly similar and costs half the price? There are several reasons to get the real deal when it comes to designer furniture. First of all, by purchasing from the authorized manufacturer you are honoring the designer and getting a piece of his energy. He (Harry Bertoia or any designer) was an artist and had specific intentions for his design. The authentics are faithful to the designer’s original vision, while knock offs are not. Secondly, you will get a quality product with customer service behind it if you buy the authorized models. We’ve heard horror stories of offices or homeowners buying the cheap versions and being disappointed in the durability and comfort of their purchases. Welds fail and the chairs are simply not comfortable. And finally, an authentic designer purchase will hold its value much better than a knock-off. One Knoll chair is always more desirable than many China-made or European copies. Would you rather have one Picasso or twenty photocopies of a Picasso?

KNOLL or HarryBertoia Foundation? If there are questions about chair care, photos rights, replacement parts, manufacturing or prices, please contact your nearest Knoll representative ( The HarryBertoia foundation ( can help with history, timeline, design aspects, Harry’s philosophy and non-material questions. For assistance on authentication of rare or unusual Bertoia chairs, contact the foundation and we will direct you to our expert Bill Shea. A fairly comprehensive chair history can be found in Celia Bertoia’s book, The Life and Work of Harry Bertoia, 2015, Schiffer. An even more extensive history of Bertoia chairs is being compiled by Bill Shea right now.

We hope these pointers will help you in your search for authentic Bertoia chairs.

Bill Shea, formerly Senior Industrial Designer for Knoll Product Development, recently retired from his own design, development and engineering consultancy, Shea+Latone, Inc.  Celia Bertoia is the Director of the HarryBertoia Foundation and author of The Life and Work of Harry Bertoia.