The body of Venezuela's Hugo Chavez is to be embalmed and put on display permanently at a military museum. How do you preserve a body indefinitely, and why is it done?

The body of Hugo Chavez is to be exhibited in glass casket in a newly converted museum of the revolution near the presidential palace where he ruled for 14 years, according to Venezuela's acting leader Nicolas Maduro.

Maduro said Chavez would be following in the footsteps of other embalmed leaders, Ho Chi Minh, Lenin and Mao Zedong.

He might also have mentioned North Korea's Kim Jong-il or Ferdinand Marcos, former leader of the Philippines. The latter's wife Imelda is keeping his body in a mausoleum in her home in the north of the country until, she says, the government agrees to give him a state funeral.

So, why are some former heads of state preserved indefinitely?

According to Maduro, Chavez belongs to his people and he will be preserved so that "his people will always have him".

Image caption North Korea's Kim Jong-il lay in state before being embalmed

The move has "some logic to it," says Margot Light, Professor Emeritus at the London School of Economics, "in order to retain the spirit of the revolution".

A change of heart Soviet leader Josef Stalin's embalmed remains (pictured) were put on display alongside Lenin after his death in 1953. But in 1961 his successor, Nikita Khrushchev, had them interred in the Kremlin Wall. Georgi Dmitrov, former communist leader of Bulgaria, was embalmed and put on display after his death in 1949. He was buried in 1990, after the fall of communism in Eastern Europe, and his mausoleum was destroyed in 1999.

"It's not as ghoulish as it might seem, it has a practical purpose for patriotic reasons and to perpetuate a movement."

Light, who visited Lenin's mausoleum in Red Square a number of times many years ago, says the experience used to be "extremely atmospheric".

"It was extremely religious in terms of how you dressed, the fact that you had to show reverence - you couldn't talk in the queue, for example."

She says that after Lenin died in 1924, there was a concerted campaign to create an ideology of Leninism, "to talk up the revolution and the movement and cement his international significance".

But the question of whether to end the cult of Lenin and bury the former leader once and for all, is one that has been raised on an almost annual basis since the 1990s.

Some Russians argue he is a relic of a different era and find the display of the embalmed corpse creepy.

Image caption People queue in Moscow's Red Square in 1963 to view Lenin's body

In Venezuela, the idea is that Chavez will be preserved "for eternity". Is this possible and, if so, how would one prepare a body so that it will look unchanged for generations to come?

Professor Sue Black, at Centre for Anatomy and Human Identification College of Life Sciences at the University of Dundee, says it is possible as long as the body is looked after well.

"The body does deteriorate - 10 years on and you don't look as good as you did," she says.

The principle of embalming is like pickling, says Black.

Incorrupt bodies The Roman Catholic and Eastern Orthodox churches regard it as a sign of holiness if a body does not decay in the normal way

Sometimes they are reported to exude a sweet smell

The bodies may be put on display, such as the body of St Bernadette of Lourdes, kept in a glass case in the cathedral of Nevers, in France

The picture above of Padre Pio was taken in 2008, six years after he was canonised by Pope John Paul II, and 40 years after his death

"It's the same principle as food. To preserve a body for the long term, you would need to create a sterile environment."

Major vessels and veins are opened, blood is taken away - it can be a food source for bacteria - and the vascular system flushed with a particular solution.

"You have to completely change the chemical composition of the tissues, and get rid of all the bacteria, so that mould and fungus can't grow," says Black.

A large volume of alcohol, glycerol - so that the body doesn't dehydrate - and formalin, which kills everything off, is flushed around the body.

"Everything is fixed, so it can't decompose - these are not very nice chemicals."

Prof Black explains that a pinkish tint is added to the formalin to give the body a realistic look.

"If you want to have a body permanently on display, you will have to address the external aesthetic - for example make up and a wig, because hair falls out."

To keep it in its best condition, you need to invest heavily, she says. Humidity and temperature need to be carefully controlled.

"For example, if a high level of alcohol is used, this can evaporate and the body can dry out, so a moist environment is needed. However you don't want to encourage mould, spores and fungus. And some flies, for example, can live on embalming fluids - so you need to 'keep the environment out and keep the environment in'."

Professor Black reckons that Chavez's body would probably need a major overhaul every three-to-four years.

In modern times, it was Russian scientists at the once state-funded Research Institute for Biological Structures in Moscow who led the way in terms of embalming heads of state.

Their services have reportedly been called on to help maintain the bodies of other nation's leaders. Since they prepared Lenin's body in 1924, tales have told of revolutionary scientific techniques, secret preservation recipes, regular baths for the corpse and an electric pump being installed inside the body to regulate humidity.

But Professor Black wonders who Venezuela will call on to perform the embalming.

"Embalming as an aesthetic has moved on in the past 20 years. But good embalming for long-term preservation is a dying art," she says. "They are not going to go in on a wish and a prayer."

In an interview in 2004, Lenin's embalmer Yuri Denisov-Nikolsky recalled how his hands trembled when he first began working on the body.

"Not every expert is allowed to restore such treasured historical objects, like a Raphael or a Rembrandt. Those who do it, we tremble. I feel a great responsibility in my hands."

According to Black, there are bodies that just simply won't take the embalming, for example, where the circulatory system is impaired.

"I'd hate to be the embalmer if this is the case," she says.