The problem with commas is that there is a bit of disagreement about when to use them and when not to. And there are also some variations in the "rules" given for the order of adjectives. Have a look at the Wikipedia write-up:
Adjective - Wikipedia, the free encyclopedia
So, I'll just give you my input based on what I know and also my preferences.
Keep two very basic rules in mind: commas should help (not hinder) reading and sentences with lengthy strings of adjectives are generally awful sentences and should be rewritten..
a) A small, blue, canvas bag. / A small, blue canvas bag. I wouldn't use any commas
b) A big, old, square, black, wooden Chinese table. I wouoldn't write this at all. You should limit the adjectives to a maximum of about three. Once you get to four or more, the sentence usually starts to become a confusing mess -- both for the writer and the reader.
c) A sharp hunting knife. Good
d) Two beautiful small old round red wax Thai candles. (Do I need commas here?) You need fewer adjectives here. It would be better to have more than one sentence and/or do some rewording, etc.
e) A dirty, torn coat. Without a comma is also OK in my opinion.
f) She writes long and flowery letters. / She writes long flowery letters (?) Both are OK.
g) A concrete glass building. (Would you order these "material" adjectives in alphabetical order? Would you please give me another example?) Your example needs the word 'and' if the building is made of both materials -- which is what I assume you mean. Without the word 'and', concrete would have to have and be understood as having a different (non-material) meaning.
Ordering adjectives alphabetically in a sentence is not something that has ever crossed my mind as a technique.
h) A practical economical car. (Under which category would you place these adjectives? Would you please give me another example like this?)I'd call practical an 'opinion' and 'economical' might be generally categorized as 'purpose'.
I realize some of my comments probably don't give you the information you were looking for, but those are my opinions.
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