Sumantra Ghoshal and Malavika Sarukkai's reel rhythms

The steps leading to the enclosed mezzanine balcony cubicle where filmmaker Sumantra Ghosal is busy at his laptop in his Central Mumbai office make it appear like an elevated sanctum sanctorum. Posters of his documentaries are displayed, not unlike images adorning walls of a temple.

The world of ad films he's worked in for four decades is far removed from that of documentaries. And he admits his latest, The Unseen Sequence (TUS) – Exploring Bharatanatyam Through the Art of Malavika Sarukkai, on one of India's finest Bharatanatyam choreographer and exponents, took him into completely unchartered territory. "I've no background in any performing art, least of all an ancient tradition like Bharatanatyam, so I am a rather odd choice to make this film," Ghoshal says with his signature self-effacing humour.

Common friends who had seen his earlier film on tabla maestro Zakir Hussain, The Speaking Hand, hoped that Sarukkai and Ghoshal would get together. "The problem was that I hadn't seen her dance because she doesn't perform often in Bombay and she didn't know my work at all. I finally watched her dance in 2011. I was quite mesmerised not only by the sheer passion and intensity of her art but also by her ability to communicate that."

"Often, there's a wall between great artistes and someone like me. Malavika broke it quite easily in the first performance I saw, and the idea to document this on film began," he says.

TUS may seem to be on Sarukkai's story, her journey and choices but Ghoshal says it's not just that. "It looks at historical forces that led from the Chinna Melam and Sadir to Bharatanatyam which democratised and evolved in the '30s, shedding its dance-of-the-Devadasi status," he says.

"I wanted to engage with an audience that is, in a sense, me before I began this project. Could I take them on the journey I undertook and share my sense of wonder at discoveries made along the way?" So, he adds, there are three strands to the film: the story of Bharatanatyam and its transformation over centuries, "the interplay between Malavika and her art form and my own journey as I react to the unfolding story — perhaps naïvely, but with emotion and sensitivity".

Artistes can be temperamental. While they get along famously once the ice is broken, it can be daunting to get there. Asked about his own experience, Ghoshal laughs, "At first, I think, justifiably so, she was quite suspicious of me. But I believe my sincerity of purpose is what finally made her agree."

And having that understanding was important since Ghoshal is known to take a long time (two years!) working on each project. "There is no script and it is about discovering things as we go along."

He emphasises total independence while helming the project. "We discussed our interpretations and respected each other's opinions. Coming as I did from Bengal and having lived and worked in Bombay most of my life, I had no clue about Tamil culture or history. I was forced to delve into Sangam literature and the Cilappatikaram! So, in that sense, perhaps it was more exciting for me than it was for Malavika. She allowed me to shoot her performances (and rehearsals) and had long conversations with me without ever attempting to interfere or influence how I was shaping the material. So much so, that she only saw the film when it was completed."

He may not have had a script and shot as he went along, but Ghoshal was clear about what he did not want. "The problem is translating ideas into work. Most people start with very good intentions and end up with not equally good films. I didn't want a biopic like earlier documentaries made for Films Division without resources or the time to investigate the subject." And he was clear he didn't want to stage dance specifically for the camera. "I decided against camera movements as they would come in the way of the work and audience. I did not want my choreography (of takes and re-takes) to distract from Malavika's intentions."

Except for one, Iccha/Thimmakka, all the poetic dance performances which punctuate the 98-minute film are actual stage shows shot during the performance, ensuring what Ghoshal calls, "the electricity of a live performance". In fact the film doesn't even once go to cutaways of musicians, singers or audiences. "I felt that that would distract from the dance itself. Also, I wanted very much to contextualise the dance from the ritual into the performative."

Why has it taken him two decades since the celebrated The Speaking Hand to make another documentary? "I think I'm plain lazy and need someone to occasionally kick me in the rear to get moving," he offers with a wink.