“The Transfiguration” shows a mysterious, singular event in Jesus’ life when he and a few disciples were alone, praying, and suddenly the disciples could see that Elijah and Moses had come to speak to Jesus. Instead of seeing their dusty, tired friend, they saw him shining with light, like the two figures who had come from heaven.
We don’t have clues about the production of this play from just seeing who produced it: the Curriers, that is, workers in leather. This may not be a case where there’s a marketing connection, nor a special connection in skills. Instead, the Curriers guild probably hired specialists to equip and run their wagon’s special effects.
In order for this play to be effective, it had to use lighting that was sudden and intense. We have some clues about what might have been done from seeing what was done in the Continental fixed-stage productions. In these, a sudden spotlight could be made with mirrors that focused the sunlight. Probably the stage was supposed to be darkened with curtains, because it was night. This would increase the contrast between dark and light.
A very simple effect could be created by sliding back a panel in the roof of the darkened stage, allowing sunlight to stream in over Jesus’ head. That’s probably too simple for a big town like York. As theater became big business carried out year after year, some men began to specialize in skills that were needed. It’s likely that the first lighting gaffers figured out how to use concave lenses to create very expensive, probably fairly small, beams of light. Glassmaking was a growing trade, and by the close of the Middle Ages, men were making eyeglasses as well as glass mirrors that were luxury goods (probably at the Paris Hilton level). My reference book suggests that on a cloudy day, candlelight might be concentrated this way to make a beam. Perhaps, but it’s hard for me to imagine a combustion flame, candle or torch, having any effect in outdoor daylight.
Other stage effects were simpler: dropping a colored or dusty cloak to reveal a white tunic on Jesus, and perhaps pulling back a curtain to allows Elijah and Moses to step forward. The wagon stage may have had a “hill” for Jesus to step onto, where the two prophets appeared. And finally, perhaps at a higher point on the stage, “God” spoke from a cloud.