One of my commentators managed to crack the case.
From Robert Louis Stevenson’s Treasure Island, the Milo Winter illustrated edition.
I had been stumped with this “crossword puzzle”.
IT SAYS:
ACROSS
1. SLEIGHT OF HAND
2. TYPE OF PUZZLE
THE REST IS TORN OFF.
I assumed (in fact correctly) that 1. indicated “MAGIC” and 2. indicated “WORD”, but I tried things like SAY MAGIC WORD with no luck. I was parsing the clue slightly wrong.
ACROSS
1. MAGIC
2. WORD
It’s indicating that ACROSS is the MAGIC WORD. So at the RAVINE where I was stuck, I just needed to SAY ACROSS.
This led me to some COAL. I was also able to DROP my LADDER here to get over to a *CAVE PAINTING* (another treasure), but obviously the coal (in its starting form) didn’t quite qualify. There was no magic machine as in Zork to process the coal, but it occured to me this might be a situation like Pyramid of Doom where the coal was just surrounding something else. Going over to the ocean and typing SWIM OCEAN gave the coal enough of a bath to get a *DIAMOND*. UPDATE: It looks like the bath part was unnecessary, just LOOK COAL is enough to cause it to switch to a diamond.
I also mentioned last time not being able to get anything off a newsstand; I was misunderstanding the situation and it’s possible to GO NEWSSTAND as if it were a room to get a copy of Hustler. There’s more detail in the comments, so I’m going to just refer to that and that say the entire business is optional.
Renga in Blue 
It sounds like you had the opposite experience with the endgame. I saw the coal, and thought, “Oh, a diamond!” All I did was LOOK COAL and it turned into the diamond. It took me a little longer to find the painting.
Ah, I must have not looked until I swam with it, I thought they were connected.
For the painting I had previously did LOOK RAVINE which mentioned a cave, so I knew it was over there somewhere.