Infra-mince, Duchamp declared, cannot be defined, but can only be described by examples, such as the difference in displaced volume between a clean shirt and the same shirt worn once, or the taste of one's mouth lingering in exhaled smoke.
Infra-mince was a new way to think about physical and temporal dimensions (decades before Mandelbrot discovered fractals). Holes in some of Duchamp's artwork link the 2nd to the 3rd dimension. Sometimes he shot the holes out with bullets, echoing infra-mince again in the delay between the sounds of the shot and the impact.
Let’s see if I have this right (and don’t bite my head off if I don’t.) The infra-mince is a fluid movement between two physical states—a transition of both difference and connection; a void both empty and full that can’t be defined. It’s a transformation, a moment of displacement, expiration dates and discontinuity, like the sound made from corduroy or velvet pant legs rubbing together when walking. It’s a gap or interval where your mind connects the dots but nothing really adds up and it becomes something completely different.
The Large Glass was originally constructed in the form we know
early last century, this glass encasement of connected ideas was
the nearest Duchamp could get to his goal. The technology was
not sophisticated enough at that time to support his interest in
the 4th dimension. He wanted to portray his Bride in the 4th
dimension and began with painterly abstractions of the figure
culminating in the flatness of glass as a material nearing the
state of no thickness or 'inframince' and therefore acting as a
signifier to the 4th dimension. He replaced traditional (thick)
paint and canvas as tools for picture making and renounced
painting, declaring his Large Glass to be "a three-dimensional
physical medium in a fourth dimensional perspective" . From
Duchamp's notes it would seem that his interest in the 4th
dimension was not aligned to the, then contemporary, 'relativity
theory' proposed by Einstein but to the idea that the 4th
dimension could be understood through geometry progressing from
the n-dimension and aligned to the mathematics of Poincaré.
"J'ai choisi exprès le mot mince qui est un mot humain et affectif et non une mesure précise de laboratoire. Le bruit ou la musique faits par un pantalon de velours côtelé comme celui ci quand on le fait bouger est lié au concept d'inframince. Le creux dans le papier entre le recto et le verso d'une fine feuille... A étudier !...C'est une catégorie dont je me suis beaucoup occupé pendant ces dix dernières années. Je pense qu'au travers de l'inframince, il est possible d'aller de la seconde à la troisième dimension"
Marcel Duchamp, quoted on: http://okno.be/?id=583