Possible Clues:

• You can't make a silk purse out of it, they say
• Unlikely source of a silk purse
• Low-quality material, idiomatically
• No silk purse source, this
• Not a silk purse source, in an old phrase
• What you can't make a silk purse out of, proverbially
• Low-quality material, in a saying
• Hardly silk purse material, in an idiom
• Bad material for a purse?
• Part sans silk purse potential