Six-year-olds Nicholas and Daniel Caffell were murdered along with their mother, Sheila - Colin's ex-wife - and grandparents in what became the notorious Essex farmhouse massacre in 1985. Though suspicion initially fell on Sheila, it was her brother, Jeremy Bamber, who was eventually charged with the killings.
With his family wiped out, Mr Caffell turned to sculpture and counselling to try to rebuild his life. And after years of painful and angry memories, he believes the piece he is about to exhibit forms a kind of conclusion.
Entitled Ying Yang, after the Chinese principle of complementary opposites, it is a sculpture of a double foetus, like twins wrapped around each other as in a womb. "It is almost a completion of my relationship with the healing process," he says. "Not a completion of my relationship with the twins, but a point of departure from dwelling on it all the time.
"It still pains me to think what happened to them, but I think I've distanced myself now from how they died."
The exhibition, Twin Images II, at the Fine Art Society in London at the end of this month, is being held in aid of the Multiple Births Foundation, which supports families with twins, triplets and more.
All works carry a reserve price so potential purchasers can place bids in a form of silent auction. Proceeds will be shared between the artist and the foundation.
Colin Caffell, whose thoughts still turn often to the boys who would now be "strapping 19-year-olds", was keen to support the charity, as he did with its previous show in 1990.
"I was very much aware when my children were alive that they were often treated as a pair and expected to be the same as each other because they looked alike."
Nicholas always insisted he was Nicholas: "He would get quite angry if people thought he was Daniel," Mr Caffell recalls. Yet Daniel had been quite happy to confuse people.
Asked whether he would be sad to sell Ying Yang, Mr Caffell replies that the image is never lost to the artist in sculpture.
"With both the children and their mother dying, that mould was broken. The lovely thing about sculpture is you can reproduce copies. You can create editions, but I can keep the artist's copy." Four editions of Ying Yang cast in bronze will be available, with a reserve price of pounds 2,250 each.
When first bereaved, making images through sculpture proved a way for Mr Caffell to cope with his pain. "It's been an important part of my survival - I think I would have gone crazy."Now 44 and living in London, he has also become a trained counsellor under the humanistic teacher Elisabeth Kubler-Ross.
Much of his time is spent with the charity, the United Pathways Foundation. Recently he has been working with traumatised children in former Yugoslavia. "The thing that was phenomenal for them was that people outside their countries cared about them." Unofficially, he has "adopted" many children in Bosnia and Croatia. "It's given me a chance to be a dad in a different way."
Twin Images II is at the Fine Art Society, 148 New Bond Street, London W1, from 23-28 February.Reuse content