‘… If you choose, you may easily find out in London what is the particular process by which the red colour of glass is produced from gold, and also in what way they would go to work to give glass a vitrified coat of gold, retaining its own colour; and whether any accident in attempting the latter might effect the former. For it has always struck me as a puzzle how so recondite an idea as that of producing a ruby tint from a yellow metal should come into the heads of the early glass-painters; and it has occurred to me that some such accident as I have guessed at above might be the key to the puzzle, for the practice of giving glass a vitrified coat of gold for the purpose of mosaic work was very common, long before the use of coloured glass in windows had been thought of, and specimens of it are to be seen in Rome of almost every age between [A.D.] 400 and [A.D.] 1000. Please not to forget this question, or be contented with vague answers. It will be likely to take some time and trouble to get at the truth, but it is curious, and there is no hurry, and you will at any rate have more opportunities than I shall. The best red colour that has been produced in modern times has been managed by a French chemist, and there is a wholesale house of his goods somewhere in Holborn. The Pope’s mosaic manufactory in Rome is curious: there are eighteen thousand shades of colour in it, which can be looked out as in a directory. Some of the imitations of pictures which they have made are so perfect that you must look close before you can see joinings and transitions of colour; and they have the advantage over every kind of painting, being mellow from the first and brilliant to the last. In St. Peter’s there are many very fine ones, copies of all the most famous pictures, and they are said to have cost 4500_l._ a piece. St. Peter’s itself is the great attraction of Rome, worth all the classics put together. I think the dome is built with all the layers of stone horizontal, so that the principle of the arch applies not to the vertical section, but only to the horizontal. I am not sure of this, but I think so.’ It does not appear, though Newman and Froude saw the Pope’s mosaic manufactory, that they saw the Pope himself, Gregory XVI. They seem to have gained their chief vistas of Roman society through their acquaintance with the Prussian Chargé d’Affaires, Baron Bunsen,[117] and his English wife, at whose house of all hospitality Sir Walter Scott, then near his end, had been the beloved guest less than a year before. Hurrell must have had his own impressions of the excellent Bunsen, with his pleasant Teutonic habit of holding up his finger and hushing the company, before he began to speak. There is no mention of our modest and all-observing pilgrims in the published correspondence either of Bunsen or of Joseph Severn, for 1832-1833.