By Daniel Dickinson
BBC News, Haydom
A saliva-charcoal liquid can help weld pieces of metal together
Twenty-year-old Tanzanian blacksmith Samweli Kangaga chews a piece of charcoal to create a saliva-charcoal liquid that he will use to join two pieces of metal.
It may seem like an old-fashioned story of alchemy, but it is a technique which has been passed down generations of the Wahunzi clan of blacksmiths living in the remote rural town of Haydom in northern Tanzania.
The liquid charcoal is spat onto a stone; a red hot piece of metal is extracted from the fire and hammered into the spit creating a tiny explosion, which signifies the welding of two pieces of metal.
"I learnt this from my father and he was taught by his father," says Samweli Kangaga. "It takes a lot of skill and I am still learning. This is a good way to join two pieces of metal."
Little has changed in hundreds of years for the Wahunzi blacksmiths. Their workshop is a shady spot under a qalelend thorn tree; bellows made from cow hide provide oxygen to keep the charcoal fire hot and it is this fire which is used to smelt the metal.
The sound of hammering rings out across the valley as the team of three blacksmiths fashion arrow heads, spears and jewellery out of the red hot pliable metal.
The workshop is run by Samweli's 60-year-old father, Danieli Kangaga, one of eight sons who all became blacksmiths.
He said in recent years the process has been modernised.
"My grandfather used to make metal by baking the local mud, but now we collect waste metal from around the district. This makes our job easier."
The scrap metal is scavenged at garages, at the local hospital or is found discarded on the ground in the form of broken cooking pots or tin cans.
The Wahunzi blacksmiths have traditionally been considered by their neighbours as lower-class manual workers and are not allowed to marry into other ethnic groups as their work is considered dirty.
But a quirk of location has made them indispensable to the local community.
The four major language groups of the African continent (Bantu, Nilotic, Cushitic and Khoisan) meet in Haydom each bringing distinct tribes and customs and importantly for the Wahunzi, a demand for different metal products.
The Khoisan-speaking Hadzabe are primitive hunter-gatherers who go to the Wahunzi for arrow heads.
The Isanzu and Iramba ethnic groups, who speak Bantu languages, and the Iraqw of Cushitic origin need kitchen utensils and spears, while the Datoga, who belong to the Nilotic language group and include the Wahunzi themselves, buy wrist and neck bracelets and spears.
"Our business is good," says Danieli. "The demand for our spear heads is increasing, because people always need weapons for self-defence."
The boom in the sale of spears may be purely anecdotal, but could reflect an increase in crime in the rapidly expanding Haydom as well as the growing number of conflicts between the different tribes over the allocation of local land.
For the time being, the Wahunzis have cornered the blacksmithing market and are making good money. An arrow tip sells for around $0.50, a bracelet $1 while a spear head can cost up to $3 - a considerable amount of money in a region of Tanzania where the average wage is less than $1 a day.
There are two blacksmith workshops in Haydom, both run by the Kangaga family.
With the increased market has come a growing reputation in the area and now Danieli is passing on his knowledge to young people outside the Wahunzi clan.
In this poor and remote region change comes slowly, so it is likely that the Wahunzi blacksmiths will continue to prosper.
Danieli believes his family will carry on the tradition for many generations to come.
"The Wahunzis will always be known as master blacksmiths and as long as traditional life continues, there will be a need for our products."