Frequently Asked Questions
7. Filling the Losses
What materials were used to make the fills?
The adhesive was the same 2-part epoxy resin, HXTAL™ NYL-1, used to bond the fragments (see Bonding). Fumed silica was used as the bulking agent mixed into it. Fumed silica is opaque, white, very finely ground and chemically inert.
Which pigments were used to colour match the filler to the blue glaze?
4 powder pigments were mixed to match the glaze: titanium white, cerulean blue, raw umber and yellow ochre. Each was first mixed separately on a white tile with a small amount of the filler, then combined. The choice of pigments and the exact amounts used to achieve a colour match with the glaze are determined by experience. The colour of the glaze may vary, even on a single object. Each area must be matched using different batches of filler.
Were all the fills made in the same way?
No. The conservator used two different types of fill on the vases. The smaller losses and cracks were all filled with HXTAL™ NYL-1 and fumed silica. However, a very few large losses that went through the thickness of the walls, such as the points of impact, required a slightly different approach.
HXTAL™ NYL-1/fumed silica filler is, by itself, too translucent and brittle to make a robust thick fill and could fail if stressed. So these fills were given a little extra strength by making an inner layer of a slightly flexible material. These were prepared in two stages. First UHU™ Plus, another epoxy resin with slightly greater flexibility and opacity, was kneaded with French chalk and titanium powder pigment to make a second filler.
A thin layer was inserted into the centre of the hole to make the core of the fill. It also acted as a backing layer for the rest of the fill. UHU™ Plus yellows faster than HXTAL, but this is not a problem as it is covered on both sides and would not be seen. Once hardened, the core fill was covered on both sides with the more translucent HXTAL™ NYL-1 filler, prepared as usual.
What tools and materials were used to rub down the surface?
The following abrasives were all used on each fill, starting with the coarsest and proceeding to the finest, finishing with micro-crystalline wax. It took weeks to rubdown all the fills to produce a smooth glossy finish.
Abrasives (coarsest to finest) :
Flour paper (grades 0 and 00)
Micromesh™ cloths (grades 3600 (coarse), 6000 (medium) and 12000 (fine))
Solvol™ Autosol chrome cleaner, a fine abrasive paste
Prelim™ Surface Cleaner, a fine abrasive paste
Renaissance™ micro-crystalline wax