New study casts doubt on common technique used in the conservation of ancient metal artefacts

Polymer coatings – including epoxy, polyurethane, and acrylics – are commonly used to protect metal artifacts from long-term exposure to light, heat, oxygen and humidity. They are lightweight, transparent, watertight, and can adhere strongly to the materials they preserve.

A new study has cast into doubt a common technique used in the integration of old metal artifacts.

The "momentous and concerning" findings, which are published in American Chemical Society (ACS) Focal Point, indicate that some transparent resin coatings react with iron-containing metals and can cause damage.

A crew from China's Beijing University of Chemical Technology created a non-invasive fluorescence imaging technique that reveals the early signs of the harmful chemical reactions. It could be used to decide on the integration state and possible dangers for other artifact preservation, decreasing the harm to the valuable artifacts.

Polymeric coatings, together with epoxy, polyurethane, and acrylics, are commonly used to shield metal artifacts from long-term exposure to mild, heat, oxygen, and humidity. They are lightweight, transparent, watertight, and can adhere powerfully to the materials they preserve.

However, there has been restricted analysis of what occurs to the coatings as they age and how this impacts the metal artifacts. This is because it is challenging to monitor what is happening at the boundary where the materials make contact.

The new 3-dimensional fluorescence imaging technique, which is described in ACS Focal Point, indicates early signs of corrosion on iron-containing metal.

The researchers coated forged iron with the acrylic resin B72—the most widely used polymer in metal artifacts—and sped up its ageing method by applying UV and warmth for 30 hours. They observed no fluorescence on freshly coated forged iron, but the fluorescence depth at the resin-metal interface increased steadily after 3 hours.

"It is surprising to acknowledge that the aged polymers can generate hazardous carboxyl teams and responsive hydroxyl radicals, inducing the oxidation and corrosion of the metal artifacts," the researchers write.

"In turn, the generated metallic ions could further worsen the ageing of polymer coatings."

They carried out the same experiment on a rusty iron coin about 1000 years old, from the Chinese Northern Tune Dynasty, and found that the aged polymer coating made the artifact rustier.

"These findings raised a timely alarm for the integration potential and possible menace of polymer coatings on metal artifacts," the authors write.

They advise that more analysis must be done to decide on how coatings can be optimised for artifact integration.

"We should strengthen the analysis on the modification of polymer coatings, together including the structural design and preparation optimisation, to exclude the existence of defects or pores in the polymers," they write.

"Employment of a particular stabiliser, or anti-ageing additives, into polymer coatings is also needed. These actions would advertise the protective potential of polymer coatings and decrease the secondary harm to cultural artifacts."output: When precious relics are unearthed by archaeologists, it’s the job of conservators to ensure they’re passed on to future generations by protecting them from further degradation.

But a new study has cast into doubt a common technique used in the conservation of ancient metal artefacts.

The “significant and alarming” findings, which are published in American Chemical Society (ACS) Central Science, indicate that some clear resin coatings react with iron-containing metals and can cause damage.

A team from China’s Beijing University of Chemical Technology developed a non-invasive fluorescence imaging strategy that reveals the early signs of the damaging chemical reactions.

They say it could be used to determine the “conservation state and potential risks for other artifact preservation, minimising the damage to the valuable artifacts.”

Polymer coatings – including epoxy, polyurethane, and acrylics – are commonly used to protect metal artifacts from long-term exposure to light, heat, oxygen and humidity. They are lightweight, transparent, watertight, and can adhere strongly to the materials they preserve.

However, there has been limited research on what happens to polymer coatings as they age and how this affects iron-containing metals. This is because it is difficult to monitor what is happening at the boundary where the materials contact each other.

The new 3-dimensional fluorescence imaging technique, which is described in ACS Central Science, indicates early signs of corrosion and rust on iron-containing metal.

The researchers coated cast iron with the acrylic resin B72 – the most widely used polymer in metal artifacts – and sped up its ageing process by applying UV and warmth for 30 hours. They observed no fluorescence on freshly coated cast iron, but the fluorescence intensity at the resin-metal interface increased steadily after 3 hours.

“It is surprising to acknowledge that the aged polymers can generate hazardous carboxyl groups and reactive hydroxyl radicals, inducing the oxidation and corrosion of the metal artifacts,” ,” the researchers write.

“In turn, the generated metallic ions could further aggravate the aging of polymer coatings.”

They carried out the same experiment on a rusty iron coin about 1000 years old, from the Chinese Northern Song Dynasty, and found that the aged polymer coating made the artifact rustier.

“These findings raised a timely alarm for the conservation ability and potential threat of polymer coatings on metal artifacts,” the authors write.

They suggest more research must be done to determine