A substance thought to be a lump of rare, potentially valuable whale vomit has turned out to be.... rubber.
Andrew Hughes found what he hoped was ambergris - produced in sperm whales' intestines - on Anglesey.
He hoped it could be worth many thousands of pounds to the perfume industry, although the value of ambergris is disputed.
Dr Vera Thoss, of Bangor University, conducted tests over two days and said it was "basically a lump of rubber".
Although unable to say exactly what the substance was, she said she believed it was probably a latex or runny rubber, which showed characteristics of being burned - possibly on a ship which caught fire.
Mr Hughes found the substance while looking for fishing bait with a friend at Porth Dafarch, near Trearddur Bay earlier this month.
But, after discovering the find was worthless, he said he could see the funny side of it.
"We weren't getting our hopes too high anyway because we're down to earth," he added.
Internet reports suggested that if it proved to be ambergris it could be worth tens of thousands of US dollars to the perfume industry.
However, Steve Pearce, a chartered biochemist and former president of both the British Society of Flavourists and British Society of Cosmetic Scientists, said there are many alternatives to the once-prized ambergris.
He added: "There may be one or two artisan perfumers who would pay some money for it - a few tens of pounds.
"I've not heard of people buying it."