There is a lot of talk about “loss” in the studio of Hans Thompson and Maxwell Malden. As art conservators, this is traditionally what they deal in: missing pieces that range in size, shape and form. Today, it’s a small chip of plastic from a conceptual sculpture belonging to a contemporary art gallery. Tomorrow, it’s the gilded oak finger of a 17th-century sculpture of St Catherine. Each “loss” comes with a fresh set of practical and ethical challenges.

Thompson and Malden founded their studio, Orbis Conservation, in 2013. The pair met at Goldsmiths and both went on to study conservation at City & Guilds of London Art School. “We’d always worked together on freelance jobs,” says Malden, who worked as a gallery technician from the age of 17. “We knew we’d work together at some point. We just didn’t think it would happen quite as quickly.”

The pair operate out of a workshop – a cavernous brick building – on an industrial estate in Greenwich, south London, flanked by car mechanics and skip-hire companies. Their work includes the restoration and redisplay of public sculptures and monuments, including the Eduardo Paolozzi mosaics at Tottenham Court Road tube station in London, and the 5,000-year-old neolithic carved Calder Stones in Liverpool. They also specialise in the material analysis and restoration of historic interiors, contemporary artworks – and just about everything in between.

Heads up: the intention is to ‘keep art alive for longer’. Photograph: Francesca Jones/The Observer

The team has recently completed their biggest commission to date: six 19th-century wooden figureheads from British naval warships, destined for display in the Box gallery and museum, a new heritage and arts complex in Plymouth due to open on 16 May.

Plymouth council’s vision for the restored figureheads was to suspend them from the ceiling. The challenge for Orbis was twofold. They needed to stabilise the badly degraded figureheads, and devise a display system that would safely suspend this surreal flotilla of 2-tonne sculptures. Fortunately, Thompson and Malden’s experience in the art industry stood them in good stead.

“As art technicians, Hans and I both had years of experience before we became conservators,” Malden explains. “If you come to conservation blind and you’re suddenly given a 14th-century marble head to work on, you don’t even want to touch it. We’d already spent years moving that kind of stuff around…”

The solution they devised was for the mount-making to became part of the conservation process: the restored pieces of the sculpture were slowly rebuilt around a new, integral steel bracket that would connect with a suspension system on the gallery ceiling. It was a process that took two years and called upon a full range of traditional and technical conservation skills.

Kirsty Walsh, a conservator at Orbis who specialises in paint and decorative surfaces, recalls the arrival of one of the first figureheads, Defiance, a bearded, classical warrior that was commissioned in 1859. “When he first came in, I think that was the closest I’ve come to thinking, this is just not possible. Every little bit of him was crumbling away. He was falling apart in our hands.”

Another, Topaze – a regal female bust commissioned in 1856 – was so badly damaged that water simply poured from the fibreglass shell she had been encased in, in a misguided effort to preserve her in the 1960s. The studio used a technique called sonic tomography to assess the internal water damage of the solid, wooden figureheads.

“We positioned nails around the circumference of each statue at regular intervals and sent sound waves between the nails. The speed at which the sound waves travel dictates the density of the wood, which suggests the degree of rot that has set in,” says Malden.

Ancient and modern: Maxwell Malden cleaning an initial test panel by Samara Scott. Photograph: Suki Dhanda/The Observer

Having established the stability of each structure, consolidants were injected into the pine for up to five months. While the wood was being stabilised, Walsh was conducting microscopic studies of paint samples in her first-floor lab, which overlooks the workshop below.

The lab is where Walsh undertakes finer conservation work. On the day I visit, it contains an incongruous gathering of projects. Alongside a conceptual sculpture from the 1980s and a 17th-century saint are pieces from the Parliamentary Art Collection. Walsh taps on a wooden freight crate. “We’ve got David Steel in here. I’m going to start working on him tomorrow. Charles Kennedy’s head is over there.” They are, of course, latex Spitting Image puppets that have started to degrade.

We’re interested in where contemporary art is going, and how conservation is going to fit into that

Walsh used microscopy to conduct paint analysis of the figureheads. Under the microscope, she shows me a cross-section of a fragment of paint taken from King Billy (a figurehead of William IV from 1833). She describes how she set the flake in resin before polishing it and placing it under the lens. The results show an undulating stratum of paints: modern blues and reds, interrupted by layers of filler and dirt, with layers of historic lead white paint at the bottom. With the use of a scanning electron microscope, Walsh is able to read the shapes of the cellular particles in the paint, which enables her to date the historic layers more precisely.

Walsh’s findings raised the question of how far back in the object’s history the restoration process should go. “As far as we could see, it was a fact that these objects were repeatedly painted in layers of lead white paint,” says Malden. “But today, figureheads are recognised as colourful objects – we might have had a bit of explaining to do if the whole collection was painted white…”

Walsh devised the colour scheme for the restored wooden sculptures by referring to a set of 1912 cigarette cards depicting navy figureheads. “I remember us all being quite disappointed when we were told they were all going to be colourful,” Malden admits. “But they were working objects,” he reasons. “They would have been painted by the sailors or ship builders themselves with fairly heavy-duty household or industrial paints that would have had an element of gloss to them, so they did have these slightly blunt colour schemes.” The matte, muted scheme developed by Walsh is anything but blunt: should the studio have replicated this glossy, gaudy aesthetic? “Hmm,” Malden muses, “I guess if you followed my logic earlier [for not painting them white], then that means we should have painted them in gloss. But we didn’t, so…”

Wood work: injecting a consolidant into a section of HMS Defiance. Photograph: Suki Dhanda/The Observer

It’s a lively argument that Malden and Thompson embrace head-on in their progressive practice, which is increasingly looking at the role of conservation in contemporary art. “We’ve always worked with living artists, and we’re interested in where contemporary art is going, and how conservation is going to fit into that,” says Malden.

Currently in the lab is a piece by the contemporary artist Samara Scott who makes sculptures from everyday materials – plastic bags, bleach, glitter, toothpaste. “Over time, her pieces start to morph,” explains Malden. These material choices can pose problems for galleries and collectors.

To ensure the longevity of Scott’s work, Orbis is drawing up a database of the objects she uses, making it easier for her to be more selective with her material choices. Malden is quick to point out that the intention is never to “stifle” the artist’s choices – it’s more a case of working out at what point in the creative process conservation become a consideration.

The studio are now keen to forge links with upcoming artists and have recently announced a residency programme for spring 2020. Orbis is offering studio space to an artist who is grappling with a particular engineering or material challenge. The idea is to explore how conservators can fit “harmoniously” within the artistic process. The intention is to keep art alive for longer.