Through mutual agreement it was released as a collaboration, becoming a top-five hit in the UK and Lewis' first to top the US Billboard Hot Dance Club Songs chart.

Glassheart received a mixed reception from critics, who praised the vocals and experimental use of dubstep and electronic music but were less impressed with the album's many ballads.

During an interview with Digital Spy, Lewis confirmed that she had recorded with Scottish DJ Calvin Harris and that Smith had been brought on board to help with production.

[8] Following Lewis' performance at BBC Radio 1's Hackney Weekend, Smith revealed that the album was 80% complete, "We've got the key tracks and we're very close.

[14] Lewis unveiled the final track listing for the standard edition on 9 September, naming twelve songs, but excluding the album's first single "Collide".

[20][33] In September 2011, Sylvia Patterson of The Guardian previewed several tracks including "Sugar" and "Trouble", both of which feature on the album, in addition to the song "Blank Page", which was written by Australian singer-songwriter Sia.

[citation needed] Digital Spy and Popjustice confirmed that Lewis spent time in the studios with producer and writer Rodney "Darkchild" Jerkins", rapper will.i.am and Polow da Don.

[51] Later following Lewis' performance at the Radio 1 Hackney Weekend in June, it was confirmed that Smith was overseeing production for the remainder of the album and was the project's executive producer.

[52] Norwegian songwriter Ina Wroldsen joined some of Lewis and Smith's studio sessions, notably contributing to the song "Come Alive".

[10] In March 2012, after extending the album's recording sessions, Lewis elaborated on the evolution of her sound, "I've got a track that's got a bit of drum 'n' bass at the end.

The track opens with a "rotating piano riff" while during the verses and choruses Lewis' vocals are joined by a strings orchestra, all of which critics noted while pointing to the strong gospel influences.

Boy, you're my favourite scar," whilst critics noted that it was full of attitude from the beginning, comparing it to songs by Barbadian singer Rihanna.

The reviewer commented on Lewis' styling: "Her long dark hair is swept back from her face, aside from her ruffled fringe, while two black stars have been carefully applied below her eyes, adding to the overall dramatic effect.

[citation needed] A newsletter to fans on 24 August 2012 mentioned the "Trouble" release and officially revealed details about a competition for aspiring musicians.

[79] During a promotional tour of UK radio stations,[86] Lewis premiered the album's title track on 19 September 2012, on Capital FM's In Demand program.

[88] On 26 September 2012, Gene Simmons' daughter Sophie Tweed-Simmons auditioned for the second season of The X Factor USA; during the judges comments on the performance, a snippet of "Fireflies" played in the background.

[90] "Colorblind" was originally performed by American rock band Counting Crows; Lewis covered the song for her 2011 release, Hurt: The EP and that version is also featured on the deluxe edition of Glassheart.

The set also included previous singles "Run", "Bleeding Love" and "Better in Time", in addition to covers of "Apologize" by OneRepublic and "Grenade" by Bruno Mars.

The audience included Lewis' parents Aural and Maria as well as models Kelly Brook, Annabelle Neilson and Indian businessman Arun Nayar.

[citation needed] Lewis performed "Trouble" live on the ninth series of The X Factor, the same show that launched her career seven years earlier.

[97] In November, Lewis uploaded the studio recording of her "Come Alive" acoustic performance which was included on the deluxe edition of Glassheart to her Vevo page.

[98] During the Stand Up to Cancer UK telethon on 19 October 2012, Lewis performed "Fingerprint" live for the first time, as well as the acoustic version of "Trouble" on This Morning.

[113] However, on 5 November 2012, at the London Oxford Street Christmas light event, Lewis introduced "Lovebird" as her new single and before performing the song live for the first time.

[121] During an interview with Digital Spy, Lewis told Tom Eames that Glassheart has a running theme about "star-crossed lovers that can't be together", and so it was likely that this idea would feature on the tour.

Ludovic Hunter-Tilney from the Financial Times found that although there was still a "preponderance of Adele-aping break-up songs", the delays in releasing Glassheart had worked in Lewis' favour by forcing her to "confront her lack of [musical] direction".

[127] Hunter-Tilney praised both the Mariah Carey-styled vocals and use of "echoing snare drums" in many of the songs, concluding that Lewis' singing "has an extra edge to it" while the music "strays out of her comfort zone".

Commending her falsetto, Corner awarded Lewis five out of five stars and ended by saying "Like many artists before her, Leona has channelled the darker side of love's grasp into her work – and the result is nothing short of spectacular.

[70] Caroline Sullivan from The Guardian newspaper picked up on the album's composition and described it as too heavily reliant on ballads, saying the issue was that it was "an area where Adele now has the advantage."

[124] The Independent's Hugh Montgomery gave the album a mixed review, saying that "obviously there's still swathes of antiseptic balladry best described as 'music to fold towels by'."

Montgomery said the album attempted to make Lewis "current again" by including songs penned by Sandé, a "Bond theme manqué" and "obviously and actually rather effectively, some dubstep".