ROBERT ZILLI: This frame appears to be made of Scots pine — Pinus sylvestris, also known as ‘deal’ — a common timber used in English frame-making. Different countries used different timber: in southern Europe (Italy, for example) they use a lot of poplar; in France and probably Spain, a lot of oak and chestnut. The English use a lot of oak and pine.

The frame is composed of sections of laminated timber — that is, where lengths of timber are glued together to roughly form the shape and the size of the frame’s profile. It's not one section of timber.

Up to four different trades would have been employed in making a frame like this: a carpenter or cabinetmaker would laminate timbers together to get the rough shape, then use moulding planes to shape the frame’s profile.

Next the frame’s ornaments were created by a carver or a sculptor. In areas of high relief, such as centres and corners, they’d insert blocks of timber that they could carve back into. Once the frame’s structure was completed, it would have to been sent to the gilder’s studio. Here the frame was prepared for gilding. Firstly, several layers of gesso [a mix of glue and chalk] would be applied to the entire frame and smoothed to a marble-like finish. They would re-cut all the fine detail — the veins in the leaves and the petals and the flowers — to sharpen it up. The next step would be to apply a layer of coloured clay called bole. This layer was then burnished to an ultra-smooth finish in preparation for gilding. The gilder applied the gold leaf to the frame, with a combination of matte and burnished areas.

So there were a lot of steps — from the rough timber moulding to the finished product. Frames of this quality were expensive luxury items that only a few could afford.

RZ: We can’t be 100 per cent certain that this is the original frame for the artwork. It is of the period — this is a British frame in the rococo style. (The rococo period in Britain was from around about 1740 to 1770.) At the time this work was painted — the early 1770s — tastes were changing from rococo to neoclassical. The flamboyance of shells, scrolls, flowers was replaced with a more refined and linear style. Though gold remained as a preferred surface finish. There are examples of early Romneys in frames similar to this, as well as Romneys in the neoclassical style. It was fashion: frames came off works, went on works — people chopped and changed all the time.

Frame-makers normally put a stamp or label on the back of the frame — sometimes a carved name or initial. The provenance of this frame could have been determined by such a label. To date we have not uncovered any evidence of this. What is known is the frame and painting are both British and stylistically appear to have been created in a very similar period.

It is not uncommon for frames to be removed from the paintings they were originally intended for. Artists such as James Whistler, who designed his own frames, wanted to prevent this from occurring; he understood the importance of the relationship between the frame and the painting. He painted his butterfly monograph on his frames, ensuring the frame would remain core to the painting. He was very much a pioneer in that area.