Alkaline substances holding up attempt to make porcelain (7)
I believe the answer is:
limoges
'porcelain' is the definition.
(I have seen 'French porcelain ' mean 'limoges' so perhaps 'porcelain' could also mean 'limoges')
'alkaline substances holding up attempt' is the wordplay.
'alkaline substances' becomes 'limes' (lime is a kind of substance. I am not sure about the 'alkaline' bit.).
'holding' indicates putting letters inside.
'up' says the letters should be written in reverse (in down clue: letters go upwards).
'attempt' becomes 'go' (go is a kind of attempt).
'go' written backwards gives 'og'.
'limes' placed around 'og' is 'LIMOGES'.
'to make' acts as a link.
Can you help me to learn more?
(Other definitions for limoges that I've seen before include "French porcelain centre" , "French city known for its porcelain" , "French commune" , "foreign city" , "French city noted for enamels and porcelain" .)