Cryptic crossword

ACROSS

1. Last of players on Welsh instrument tuned above the pitch (5)

4. Its application is clearly made to fade out right inside (7)

8. Grilling or training toe to wriggle (13)

10. Once and again, two have nice union on leaving (5)

11. Knot that has been done wrong (4)

12. Card having any desired value is so uncivilised (4)

16. Turn out to be all-time teenage leader (5)

17. Before anything else, it’s object number one (3,5,5)

19. A group studying remains that are to be sorted out (7)

20. Having been responsible for brushwork, Degas finally cried (5)

DOWN

1. Where pools may be entered without putting pen to paper (8,5)

2. Painting of Round Table monarch − top half only (3)

3. Chaste quality turning up, it may be found in the railway (6)

4. There’s nothing − nothing − four can turn up that’s bowed (6)

5. Bookish person may be the one who corrected the press (6)

6. Copying one, you’ll find me getting it at four inside (9)

7. Her hut-wedding somehow turned out to be a weighty affair (13)

9. ‘Why,’ where Hilary is concerned, the holidays follow it (3-2-4)

13. Intend to make a pattern (6)

14. Minor Saints one may look lecherous about (6)

15. America, in short, sets forth (6)

18. Finish making cake, none being cut if no impression is made (3)