Drop a Duralex glass and it will most likely bounce, not break. The French company itself has tumbled several times in the past two decades and always bounced back, but never quite as spectacularly as when, earlier this month, it asked the public for money.

An appeal for €5m (£4.4m) of emergency funding to secure the immediate future of the glassworks took just five hours and 40 minutes to reach its target. Within 48 hours, the total amount pledged had topped €19m.

François Marciano, 59, the director general of Duralex, said the response had astonished everyone at the company. “We thought it would take five or six weeks to raise the €5m. When it reached nearly €20m we had to say stop. Enough,” he said.

As a staff cooperative, €5m is the maximum Duralex can accept in public investment under financial rules.

Beloved French brand

Mention Duralex to any French person and they will be transported back to childhood and a school canteen. The brand evokes a mix of nostalgia and pride and is a symbol of French patriotism and industrial savoir faire.

“We’re like Proust’s madeleines,” Marciano said. “The French people want to save us. They are fed up with factories closing and the country’s industries declining.”

At the Duralex factory on an industrial estate in La Chapelle-Saint-Mesmin on the banks of the Loire just outside Orléans, Marciano says he and his colleagues are “floating on a cloud” after the appeal.

Eighteen months ago, Marciano oversaw a staff buyout of the company, which had been placed in receivership for the fourth time in 20 years. Today, 180 of the 243 employees are “associates” in the company.

Suliman El Moussaoui, 44, a union representative at the factory where he has worked for 18 years, said the appeal had prompted “a tsunami of orders, so many that we’re struggling to keep up. Every time the company is mentioned on the television or radio we have more orders. It’s been amazing.”

Inside the factory, a simple but magical alchemy takes place. A mix of sand, soda ash and limestone, the exact proportions of which are a closely guarded secret, is heated in a vast overhead oven to 1,400C. Glowing globs of molten glass drop into iron casts that are blasted with a flame of gas. The red-hot glass is instantly pounded into shape, sprung from the mould, snatched by metal pincers and placed on a conveyor belt.

The process has changed little since Duralex – which is said to take its name from the Latin expression Dura lex, sed lex, meaning “the law is harsh, but it is the law” – opened in 1945. When the Guardian visited, the production line was turning out small clear glasses in the Provence range.

A worker brandishing tongs lifted a glass to the light to inspect it for faults. During a production run, more than a dozen samples of whatever is being made – glasses, plates, bowls – will be randomly removed and subjected to stress tests. In the quality control room, they will be heated to 150C then plunged into cold water to see if they resist a thermic shock, and dropped from the height of a kitchen counter on to a metal sheet to see if they shatter. They will be tested for stackability and then weighed and the glass thickness measured. If they pass, they are thrown in a bin and the production line is given a thumbs up. If they fail, everything stops and the machines are recalibrated.

‘The ultimate drinking vessel’

It is not known who invented the company’s trademark Picardie glass, the tumbler used in school canteens with a thick curved rim and semi-fluted shape that first appeared in 1954. The British design guru Patrick Taylor has ranked the Picardie alongside Levi’s jeans and the Swiss Army knife as an icon of modern design. Taylor describes it as: “An object whose form gives the impression it was discovered rather than designed. It is the ultimate drinking vessel created by man, and of its type cannot be improved.”

Duralex says its glass is microwave, freezer and dishwasher-safe and will not turn cloudy or lose its colour, which is in the glass rather than on it. When they do break, Duralex glasses shatter into small pieces rather than shards, reducing the injury risk.

Joël Cardon, 59, who has worked at the factory for 35 years, said the soaring cost of gas and electricity were the firm’s largest and most worrying expense.

On his screen, the oven containing the liquid glass showed a temperature of 1,440C. It can never be allowed to cool or the glass will solidify. Another screen showed the factory was using 360 cubic metres of gas an hour. According to the regulator Ofgem, the average UK house uses 97.3 cubic metres of gas a year.

Last weekend, potential investors were asked to come good on their promises on a first come, first served basis. They will be issued with securities that pay 8% interest over seven years but give no company voting rights. The maximum investment was set at €1,000.

“We want to involve as many people as possible but with almost €20m in pledges obviously some people will be disappointed,” Marciano said.

Since the company became a staff cooperative, turnover has increased by 22% and Marciano said he hoped Duralex would be breaking even by 2027.

The €5m raised will be used to modernise the factory and develop new products. These include a partnership with the Élysée presidential palace shop to sell a set of three of its Gigogne glasses in red, white and blue, marked RF for République Française.

Duralex plans to commission moulds to make “pint” glasses with a measure line for British pubs and bars and the US, both regions identified by the company as untapped markets.

“Selling abroad is more difficult because there isn’t the same nostalgia for Duralex as there is in France,” said Vincent Vallin, the head of strategy and development. “Interest in the company is high and this is positive, but now we have to focus on increasing sales.”