Hello " ". The floor in the photos indeed does not appear to be acceptable for approval. The waves in at least the first photos can no longer be seen in the following shots. Yes, there was and still is, among other things, a note in DIN 18365 that evaluations in backlight are not permissible. But here we are dealing with low-level windows, so that statement does not apply here. Anyway: from my point of view, the refusal of acceptance seems justified. The yellowing is also worthy of complaint if the original sample, regardless of whether such a small sample area produced under laboratory conditions can represent a large area, does NOT exhibit yellowing to a noticeable extent as present in the object. What happens next? Primarily, this is a legal matter. You must send the contracting party a written notification of defects with a deadline for remedy (by registered mail). The letter must already include the term "notification of defect" in the subject line. The usual process then leads to a legal dispute with expert assessment. You now have three options: 1.) You grit your teeth and accept (which also means: pay) or 2.) You have the floor inspected by an expert familiar with the subject of "design floors," whereby all parties should be invited, 3.) You let it come to a legal dispute and hope that the expert appointed by the court also has the necessary expertise concerning such mineral gradient coatings. And one last word on the topic "this is still within the tolerances": Such assessments, as required here, should be left to neutral observers (publicly appointed and sworn experts). A company expert is all too often subject to pressure from their own employer. ------------------------- Best regards and a "lucky hand" for the further proceedings: KlaRa