Full Idea
Paintings and sculptures do not work within a notation; hence, there is no copying of an original that would preserve its originality. A copy of a painting is a copy, not an instance of the original.
Gist of Idea
A copy only becomes an 'instance' of an artwork if there is a system of notation
Source
Nelson Goodman (Languages of Art (2nd edn) [1968], p.212), quoted by Alessandro Giovannelli - Nelson Goodman (aesthetics) 2
Book Reference
'Key Thinkers in Aesthetics', ed/tr. Giovannelli,Alessandro [Continuum 2012], p.173
A Reaction
Sounds conclusive, but isn't. Is a poetry manuscript a 'notation' or an original? Why is an etching plate a notation, but painting on canvas is an original? Can I create a painting specifically so that it can be copied (by my students)? Intention matters.