Topic: How was the black covering done on this Derbyshire vase?

[neilh]

This well known John Derbyshire vase RD300300 dates from 1876.

It is usually seen in black, matt or gloss, but also in plain or frosted.

There appears to be something odd about the black covering of this piece. Usually, black glass from this period is a very dark amethyst, which may look deep purple or red under strong light.
This one is different. It looks like an amethyst / puce item which has had a black covering applied in some way.

A close up shows a black layer over the top, which can flake off to show the puce underneath.

I've recently seen a puce one without covering, which is a previously unknown colour for this registration.

Actually I think the "frosted" version is really a satin finish, or a coating of some sort. Maybe this was made by dipping a plain one in acid?

Does anyone know what process is being used here for black and white?

[Ekimp]

I might have misunderstood but I can’t see the “black layer over the top, which can flake off to show the puce underneath”. Is that what the last photograph is showing?

To me, it looks like a solid dark colour that has been acid etched to give the matt frosted finish. The frosted surface appears slightly lighter than the unfrosted glass. Probably as the frosted surface defuses the reflected light or something.

Your last photograph looks to show a flake chip on the right (so no frosting, glass looks darker). On the left, it looks like an elongated bubble that was very close to the surface that has broken through after acid frosting. The bubble has only broken through on the left hand side where you can see the dark glass as the inside of the bubble wasn’t frosted. On the right hand side of that bubble you can see it is still covered with a very thin layer of glass (where it is even lighter as the glass there is very thin with the bubble beneath).

John Northwood developed white acid for frosting in the U.K. in the 1860s. Ref Hajdamach page 184.

[neilh]

Thanks, I guess this is a side effect then of how Derbyshire was achieving the matt and gloss look of certain pieces with acid. It is relatively unusual for the Manchester factories to use acid frosting for pressed glass, most was abraded, maybe the fancy stuff was acid frosted more often. Not many examples to check, though there are several opaque Landseer lions which may have undergone the same process.

[Ekimp]

I don’t know much about pressed glass but I believe the abrasion type of frosting was the preferred method if the surface was suitable (smooth vases etc) even after acid frosting had been developed.  Complex surfaces like your vase, acid frosting would be easier (if available). There is a Rebecca compote from American that has been discussed where the same item has both methods of frosting. The complex figural bases are acid frosted but they still chose use abrasion to frost the smooth ribbons on the bowl, indicating to me abrasion was better where the surface allowed. Discussed here: https://www.glassmessages.com/index.php/topic,70868.msg398902.html#msg398902

[neilh]

Yes, good point. I've been checking my pressed glass recently for abraded vs acid frosted, and it is surprising how much is abraded.
One of the few that was not is this creamer from Robinsons of Warrington c1870. A complex pattern.

[Ekimp]

One of the few that was not is this creamer from Robinsons of Warrington c1870. A complex pattern.

That’s a good one, it looks like it has actually been abraded. If it was acid etched they would have to mask the low areas of the pattern (it doesn’t look like the low areas are frosted). The clincher is the mould seam on the neck where one side has missed frosting.

I believe this type of design would have been spun in a lathe as the roughing tool was applied. The glass on each side of the mould seam was at different heights due to the mould not closing perfectly. The different heights has allowed the roughing tool to bridge the gap, leaving an unfrosted area on the low side. I expect you will see scratch marks, all parallel going horizontally around the circumference. This should be especially apparent at the interface between frosted and not frosted areas at the seam, where the scratches will feather out. There might also be very small nibbles on the edges, such as at the Greek key, which will indicate which way it was spinning when abraded, the tool will have knocked off the nibbles on the left or right. If this was randomly abraded then it’s unlikely that the area next to the seam would have missed frosting. Although it is a complex pattern, they have only frosted the smooth parts, if that makes sense.

[neilh]

ok I will have to view that one again. It is quite difficult to tell on some pieces if there are no horizontal score marks, like on this one.

[Ekimp]

Thanks for showing it.