For a building such as the Minster, which dates back to the 10th Century, its many design features have been in almost constant flux, with new generations adding their own touches or nature eroding the facades.
Snell said: “You can tell when certain parts have been added on at a later date, or renovations and restorations have happened, because the style does change.
“We can tell almost instantly when the Victorians have done something, because they actually used a different type of stone in a lot of areas.
“The grotesques are quite different from the Victorian period to the medieval period too.”
Grotesques are carvings, usually of demons, dragons or other mythical creatures, that were often used to decorate cathedrals and churches.
The carvings were intended to protect buildings from evil spirits.
Grotesques are sometimes confused with gargoyles, which look similar but contain a water spout through the mouth.
York Minster has, in the past, produced new grotesques created by skilled stonemasons.
