Mephisto

[foxspur]

OK I surrender
15ac Piece work went back in Scottish zinc, loosely (7)
I have T??EN?G

17ac Char's language beginning to naff off (5)
I have ?OG?E Is it TOGUE (tongue without n)?

6d Early supper, poor, fails to finish imbibing what's essential to espressos (7)
I have MEA???A If Togue is right it would be MEA?T?A
Poor is meagre?? Is CA caffeine, essential to espressos??

Finally 21d Bit of string dependant found in apron a welcome surprise (7)
I have ?IE?PIE
This depends on 34ac being AERIE, or AYRIE

Goodbye for another week, bar the thank yous

[Rollo]

15a TUTENAG - a zinc alloy.

17a A TOGUE is a char (fish).

[Rollo]

21d is REIMPIE - a piece of string.

I can't yet find a word that will fit your letters for 6d.

[Harry-Wragg]

meat-tea is an early supper but I can't see the connection with espressos

[foxspur]

Thanks Rollo
6d is now MEATT?A
The last A depends on the answer to 24ac being CHASMIC
The clue is Choir like sound instrument in opening
The CHSIC are definitely right, only the A and M could be wrong.
Any ideas?

[foxspur]

Thanks Harry it must be meattea, I didn't see your answer before thanking Rollo.

[Rollo]

Chasmic is OK

(choir) CH + (like) AS + (microphone) MIC

[crockshard]

Re 'meattea', I assume it is a 'teat' that is essential to espressos!