This post was contributed by Helen Barrell, a writer of historical fiction (and non-fiction)

The colour green has long been associated with the festive season. The shade of holly and ivy and fir trees, it reminds us that after the dark days of winter, spring will return. But green is associated with something else, too - poison. More specifically, arsenic. Our ancestors had many uses for arsenic, using it to control unwanted rats and mice in the home, and its green pigment made wonderful dyes, known as Emerald Green or Scheele's Green.

Alarmingly, some people used Scheele's Green as a food colouring. In Northampton in 1848, one man died and several were left seriously ill after blancmange served at a dinner was coloured with the pigment. The confectioner who sold it was imprisoned for manslaughter because they hadn't been clear about the quantity of dye that would be toxic ( Northampton Mercury, 22 July 1848). No one pointed out that using arsenic to colour food, even in small amounts, might not be a good idea, perhaps because tiny quantities of it were thought to be good for you.

One day in December 1871, a professor of chemistry in Glasgow was swinging his way along a street in the city, the shop windows bulging with Christmas displays. He paused outside a bakery, and one cake in particular caught his eye. Its vivid green colour was, he believed, "suspicious." He bought the cake and, presumably not eating any of it, tested it in his laboratory. He found arsenic. The next day, he sent two of his assistants to the same bakery, and they each bought a green cake, both of which also turned out to contain arsenic. The observant professor went to the police, who searched the shop and found another green cake on the premises. The bakery's owner admitted that he had intentionally painted the cakes with emerald green, but he added that the dye was perfectly legal. It does not seem that The Adventure of the Green Christmas Cakes led to prosecution. ( Dundee Courier, 18 Dec 1871).

Did Mrs Beeton's Christmas Plum Pudding contain arsenic? Wellcome Library, London

In 1903, The Lancet did its best to rouse Christmas spirits by warning everyone that the festive period was fraught with danger. Costumes worn at amateur theatricals, covered in cotton wool to represent snow, were fire hazards, as were celluloid tree decorations and children's toys. If this wasn't enough to put a dampener on proceedings, they reminded the public that toys might be covered in poison-pigmented paint, and that coloured Christmas tree candles had, in the past, been the source of arsenical poisoning. The report was printed widely in local newspapers, who prefaced it saying it was a "doleful view". (Western Daily Press, 14 December 1903)

In Luton in 1900, the Board of Guardians were discussing what could be done to provide Christmas cheer in the workhouse. Few venues could have been gloomier. The Master had made a list, which included 14 pounds of tobacco and half a pound of snuff. One guardian protested that a huge amount of tobacco was being smoked in the workhouse, whereas another stated that the inmates should be allowed a few luxuries at Christmas. Another of them quipped that they hoped there would be no arsenic in their Christmas beer. (Luton Times and Advertiser 21 Dec 1900) He may have been referring to the Manchester arsenic-in-the-beer epidemic of 1900 to 1901; caused by brewers using contaminated barley, it led to a condition known as "alcoholic neuritis."

They hoped there would be no arsenic in their Christmas beer

But the danger lingered after Christmas. Twelfth Night, on 6th January, is observed in the UK as the day you take down your decorations – by then, people have gone back to work and school, and dreary January will have done its best to extinguish whatever remained of the Christmas spirit after the New Year's Day hangover. In the church calendar, Twelfth Night is the Feast of the Epiphany, and in the nineteenth century it was also known as Old Christmas, because it's the day that Christmas Day used to fall on before calendar reform in 1752 (to confuse things even further, some people celebrate Old Twelfth Night on 17th January). A Twelfth Cake would be eaten in celebration, sometimes a grand confection with elaborate icing, and a detailed tableau of figures. Queen Victoria's Twelfth Cake shows how elaborate it could be, with what looks like a miniature party in full-swing. But in 1853, two children died after eating the ornaments on a Twelfth Cake. Professor Alfred Swaine Taylor – one of Britain's leading forensic scientists – found that the paint used to decorate the ornaments contained high levels of arsenic. (North Devon Journal, 3 Feb 1853)

Queen Victoria's Twelfth Cake

These days, you're unlikely to be visited by the ill-effects of arsenic at Christmas. Still, if anyone offers you a slice of suspiciously bright green cake, it might be sensible to refuse.

what mysteries will you solve. start exploring our records for FREE

More sweet treats... A Christmas pudding for 7000