The secrets of the Middle Ages' leading special-effects experts have been pieced together, writes Steve Farrar.
They reveal how England's medieval technicians added magic to dramas with a mixture of mechanical ingenuity, pyrotechnics and optics.
James Stokes, professor of English at the University of Wisconsin, found evidence of religious spectacles staged at Lincoln Cathedral in the 15th and 16th centuries.
Church records refer to the keeper of the orlege, a construction of wood and metal that was raised and lowered during celebrations. They also hint at containers being lifted towards the roof of the cathedral, and there is evidence of the involvement of roof openings, winches and pulleys.
Professor Stokes has fleshed out these bare bones with more detailed accounts of similar dramas in Florence.
These featured choristers dressed as angels descending through roof apertures on board circular structures. While the heavenly host hung in mid-air, a smaller contraption called a mandorla emerged to carry an archangel to the floor. He then approached Mary and accompanied her on her ascent.
Furthermore, every flap of an angelic wing caused lights to dim and flare through the use of hidden strings and shuttered candles, while doves were released from hanging baskets.
"It was all quite wonderful. This level of the technical skill has been underrated throughout history," Professor Stokes said.
The historian also found that Lincoln's guild of cobblers used a variety of reflecting surfaces to create patterns of intense light around a manger inside a darkened chamber during the Bethlehem Pageant.
Philip Butterworth, dean of research at the University of Leeds faculty of music, visual and performing arts, suggested one special effect mentioned in the stage directions of the medieval Croxton play of the Sacrament - "here shall the cawdron byle, apperyng to be as blood" - could have been achieved by adding vermillion powder or oil to a small fire to produce red smoke.
The findings were presented to the International Medieval Congress in Leeds this week.