[....] Las claves
The advantage of this new carving method is shown in the sketches in photo 34; in A, we can see a bosstone which has been drawn using as reference the tangent plan, in B the bosstone’s projection on that plan, and, lastly, in C we have the bosstone carved on the tangent plan.
As it has just been said, the carving of the tilted bosstone draws from its projection on the tangent plan. The photo 35 shows how this projection is designed on a block containing the volume of the voussoir, then its carving is undertaken in the same way as it was done with the vertical bosstones.
We have previously mentioned an interesting peculiarity: although the bosstone is tilted, the subsidiary rib remains vertical (photo 32). This particular seems to complicate the key carving, but in fact it can be done quite easily. If we again have a look at photo 34C, we can see that the distorted template of the subsidiary rib seems to lay its trasdos on the tangent plan. Let us proceed the same way with the carved piece. When placing the subsidiary rib’s template standing on the horizontal plan, which is really the tangent plan, the subsidiary rib will remain vertical, in its correct position, as photos 36-39 show.
The carving of the tilted boss starting from the tangent plan projection seems to approach Gothic stonemasonry to the sphere’s stereotomy. Vandelvira, in his Treaty, presents us this way of tackling his Gothic vault’s keys’ carving (photo 40). [....]
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