We talk to Manchester-based sculptor Nicola Ellis as she goes “head to head” with Aura Satz in this Manchester Weekender exhibition.

You catch your first glimpse of it as you turn the corner onto Hewitt Street and gaze down towards the Bridgewater Viaduct. Its creamy white prong stretches across the ground, contrasting with the steely façade of the railway bridge opposite. As you get closer, the sheer scale of the creation becomes apparent: a globular arm reaches almost six metres into the air and looms precariously over the Deansgate cobbles.

No, this isn’t the subject of a 1950s sci-fi movie, it’s “Porites,” a sculpture by Nicola Ellis that currently resides in the double height space of Castlefield Gallery’s ground floor, confronting visitors through the panelled windows. An L-shaped frame coated with expanding foam, the specially-commissioned piece forms the centrepiece of Head to Head, which opens at the gallery this week. “A lot of the time it’s very surprising what the work looks like, even for me,” says Ellis. “All of a sudden it’s there, and you realise that this is what it is and you have to deal with it.”

“Porites” features alongside works on paper by Ellis, as well as a black box film installation and selection of ink drawings by London-based artist Aura Satz. Presented as a “head to head” between an emerging artist (in this case, Ellis) and a more established one (step forward, Satz), the exhibition may be structured as a debate, but gallery director Kwong Lee sees it as more of an open-ended discussion. “We use words like ’emerging’ and ‘established’ but fundamentally, artists are artists,” he says. “We’re providing a platform to show new work and share ideas.” Nor does the exhibition attempt to force links between the works on display: neither artist had experienced the other’s work before their involvement with the gallery. “We’re not saying that Nicola and Aura’s work is similar,” explains Lee. “We’re saying, look at the two practices and see how they may relate. The show is about being suggestive rather than making explicit connections.” The thought of exhibiting with an artist whose work has appeared at Tate Modern doesn’t seem to faze Ellis. As someone who is still trying to “get to the crux of what it actually is that I do,” she sees the exhibition as an important learning opportunity. “I just can’t wait to meet Aura,” she says. “The more people that you can meet with more experience than you, the better.”

Nicola’s sculptures always make you ask, ‘What is this material?’

If the “head to head” element is to be found anywhere, it’s in the dialogue between Ellis’ works on paper and her sculpture. The Manchester-based artist has shown 3D work at the Bureau and Paper Gallery, but this is the first time her drawings have formed part of an exhibition. “Works on paper are much more personal than sculpture,” she says. “They’re a thing that I do every day; they show the inner workings of my practice.” Ranging from brief stains on paper to those with more developed textures, the pieces reflect the focus on materiality in Ellis’ sculptures.

The exploration of sometimes incongruous materials (the “Peregro” sculpture featured in Cornerhouse’s FOUR exhibition earlier this year was made of silicone, wrought iron and Polyurethane) is a recurrent theme in Ellis’ work. “Nicola always makes you ask, ‘What is this material?’” says Lee. “There’s a dialogue between the different types of material; hard and soft, ephemeral and solid.” “Porites” encapsulates this paradox; its internal steel frame is deceptively lightweight but the mix of expanding foam, clay and toilet paper combine to create a rocklike coating.

The natural world also provided the inspiration for the sculpture’s name. Porites are a genus of coral with a similar chemical makeup to that of human bones. Because of this eerie chemical similarity, they can be used as a bone graft substitute and inserted into damaged parts of the human body a kind of coral scaffold. “The porites get absorbed and moved around to the rest of your skeleton,” explains Ellis. “I thought that was great, especially since the genus do actually look a lot like my sculpture.” Standing in the presence of “Porites,” the thought of a small substance being absorbed into a larger, alien one seems strangely appropriate. Castlefield Gallery, 2 Hewitt Street, M15 4GB, Wed-Sun 1pm-6pm and all weekend  during Manchester Weekender, free. The gallery also hosts a special after hours opening on the Thursday of Weekender.