Whether to punctuate between two or more adjectives preceding a noun can be a difficult decision to make. Consider these points next time you are confused about what is appropriate.
In the sentence “Many great artists were not recognized as such during their lifetimes,” many and great, though they are both adjectives, are not coordinate. The notion of many artists and the notion of great artists are not equivalent, because great is essential; the reference is not to any artists, but to great artists, and many modifies the phrase “great artists,” so no punctuation precedes the phrase.
This is true regardless of how many adjectives precede the noun, if they are essential to describe the noun. “Many great Renaissance artists were not recognized as such during their lifetimes” does not require punctuation, either. However, if more than one adjective modifies a noun phrase such as “great artists” (or “great Renaissance artists”), or an adjective in that role is repeated, the two (or more) adjectives should be separated by a comma: “Many, many great artists were not recognized as such during their lifetimes.”
Also, when we speak of a wide stone floor, we don’t punctuate the description, because the adjectives are not coordinate. Wide and stone are two ways to describe a floor, but the composition of the floor is the pertinent point, and its expanse is simply an additional detail; that’s why we wouldn’t refer to a stone wide floor.
The distinction between coordinate and noncoordinate adjectives is usually clear, even if in various examples, different adjectives precede the same noun. In many cases, the noun is a standing noun phrase.
Consider the noun table. If it is preceded by low, we understand that “low table” is not a standing noun phrase. (You won’t find that open compound in a dictionary, because it hasn’t acquired a permanent utility in the English language; “low table” does not conjure a uniform image in our minds.) The same is true of “long table.” Therefore, when a table is described as long and low, we write “long, low table” using the comma to signal that long and low are equivalent in modifying table: They describe two characteristics of the table. (The order in which various types of adjectives appear is fixed; see this post for a discussion of the royal order of adjectives.)
However, when table is preceded by dining, we understand that “dining table” is a standing noun phrase. Though dining tables differ in appearance, the concept, as opposed to long or low tables, is precise; a table can be more or less long or more or less low, but one cannot discuss how dining it is. Therefore, long and dining, and low and dining, are not coordinate, and therefore we write “long dining table” “or low dining table” (or “long, low dining table”).