Part of Fondation Constant's mission is to protect the legacy of Constant Nieuwenhuys. The foundation is usually informed when works on the market are thought to be a copy, false or misattributed to Constant. Each situation has different implications.

  • First situation: Infringement on copyrights - an existing work of art is copied by someone, who, without prior permission of the copyright holder/Pictoright, reproduces the work and/or makes the work available to the public-with the artist’s name or his own name. This is considered a breach of or infringement on copyright and will therefore be handled by the organisation that handles the artist’s Intellectual Property rights.
  • Second situation: Misattribution - a work is mistakenly attributed to the artist. Even though there might not have been the intention to deceive, these works must be unveiled to avoid the illusion for owners or potential buyers that the work represents a certain value as if it were an authentic work from the artist.
  • Third situation: Forgery - a work of art is created with a deliberate intent to deceive. These works are usually presented falsely as a product of another time and/or artist. This could concern copies of existing works of the artist (falsification) or newly created works in the style of the artist as a consequence of which the work can be misattributed to the artist. Both situations are considered a forgery and a criminal act and will therefore be handled by the justice department and Pictoright.

The negative effects of these dealings have an impact both on individuals involved, the value of the works of the artist, and on the art market in general. Fondation Constant is supportive in the fight against these activities. We have close ties to both Pictoright, the Dutch Criminal Investigation Department for Art Related Crime and parties such as the Art Loss Register, who are all dedicated to eradicating  criminal activities from the art market.

On this page we will post information on the doubtful art works we encounter and where we have encountered them. To avoid law suits we will refrain from mentioning the specific parties involved.



NB: Fondation Constant does NOT give out certificates of authentication. When a work adheres to our guidelines for authenticity we will add it to out digital catalogue raisonné.

Tips when buying art

  • Ask for documentation on the work of art. Original works usually are obtainted through offical channels and come with invoices, catalogue/exhibition listings and are mentioned in art books.
  • Ask for a provenance. Original works are usually easily traced back to their source, this list of previous owners is called a provenance. Original works of art come with a provenance.
  • Do a background check on the seller. Is the seller a well respected art gallery that is well known for selling the art of this artist?
  • Do a google search on the prices. If the selling price seems too good to be true compared to works you find at the well renowned galleries, it probably is. However, above a certain price level most galleries do not make their prices public.
  • If a work is sold as assigned to... instead of by... it usually means there is reasonable doubt about the work's origin.
  • If buying online, check the Terms and Conditions of the online resellerThey might already indicate that they are not responsible of the authenticity of the works they offer!

These are some rules of thumb that should give you an indication of a works authenticity. If after this checklist, you still are unable to reach a conclusion, you can contact Fondation Constant for an assessment. Go to Assessment, for more information.



Fondation Constant is a not for profit organisation and your donations are always welcome and ever necessary: paypal.me/FondationConstantNL

Fondation Constant cannot be held responsible and/or liable for any damages, costs, expenses, loss or grievances incurred by publication or the use of the content published with regard to "Copyright Infringement, Misattribution and Forgery" on this website.

Fondation Constant will only publish information on such works if, after expert research with regard to the work, the case etc, Fondation Constant is of the opinion that such work is not authorised or authentic. However, these publications are to be considered the opinion of Fondation Constant only. Fondation Constant does not accept any liability for damages, costs, losses etc. arising from such publication.

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Title Year Technique Category CID
2012 Watercolor on paper, 1975 No Title/Horses..? 1975 Watercolour Forgery 7413
2012 Sketchbook, signed, no year I Sketchbook 1980 Drawing Forgery 7412
2012 Gouache on paper, 1949 No Title/Not Even Close to Cobra Figurines 1949 Watercolour Forgery 7411
2012 Watercolor on paper, no date Another Copy of a La belle noiseuse 1990 Watercolour Copyright Infringement 7410
2012 Watercolor on paper, no date Copy of La Mère Noël 1983 Watercolour Copyright Infringement 7409
2012 Construction, no year Another Copy of Construction with Transparant Planes 1956 Construction Copyright Infringement 7408
2012 Gouache on paper, 1960 Poor Copy of "Interieur met Laddertjes" 1960 Watercolour Copyright Infringement 7407
2013 Gouache on paper, no year No Title/Abstract with Weak Colours 1961 Watercolour Forgery 7406
2013 Gouache, no year No Title/Decorative Shapes 1980 Watercolour Misattribution 7405
2013 Watercolor on paper, 1975 Copy of Plaisir et Tristesse d'Amour 1975 Watercolour Copyright Infringement 7404
2013 Charcoal, ink and gouache on paper, no year No Title/White Figures 1951 Drawing Forgery 7403
2013 Oil and pencil on paper, 1948 No Title/Creature 1948 Oil painting Forgery 7402
2014 Mixed technique on paper, 1969? Another Copy of "Interieur met laddertjes" 1969 Watercolour Copyright Infringement 7401
2014 Gouache on paper, 1951 No Title/Two Poorly Drawn Figures 1951 Watercolour Forgery 7400
2014 Watercolor on paper, no year Another Copy of Femme et Enfant 1997 Watercolour Copyright Infringement 7399
2014 Watercolor on paper, no year No Title/Grey Figures 1997 Watercolour Forgery 7398
2015 Oil paint on pressed plate, 1954 No Title/Bad Cobra Imitation of Sorts 1954 Oil painting Forgery 7397
2015 Oil on cardboard, 1955 No Title/Imagery Unclear 1955 Oil painting Forgery 7396
2015 Oil and watercolor on canvas, no year No Title/Green Red White 1980 Watercolour Copyright Infringement 7395
2015 Drawing with pencil on paper, 1961 No Title/Construction 1961 Drawing Forgery 7394
2016 Collage with watercolor and pencil, 1969 Umpth Rendition of Figuren in ruimte 1969 Collage Forgery 7393
2016 Oil on canvas, no year II No Title/Pierrot 1980 Oil painting Forgery 7392
2016 Watercolor, 1949 No Title/Landscape? 1949 Watercolour Forgery 7391
2016 Gouache on paper, no year Rendition of Femme Terrible 1949 Watercolour Forgery 7390