Loetz and Karl Goldberg

Many, many years ago, when there were still small antique shops all over New York City, I happened to stumble onto a magnificent vase that I just had to have: 14 inches tall, 1/4 of an inch thick glass, with a grainy yellow surface and a complex decor of etched wild birds showing silver deposit remnants. There was just one problem, said the dealer. It had a fake Loetz signature. The signature in question had not been crudely added at a later date, as is usually the case with so many Loetz and non-Loetz pieces. It was actually embossed on the bottom of the glass as part of the mold, for the vase had no pontil. I decided to go for it. This is a picture of the front:
 Pictures of the back and the signature at the bottom: 
Much later I found a vase with the same decoration in an auction catalog: same height, hourglass shape, but thinner glass walls. It had a Cross of Lorraine in gilt at the bottom, and was identified as Daum Nancy! I was lucky to find yet another piece, a small bowl I had for a while until I decided to part with it. And then, at our local flea market, I found a bargain: another vase, in emerald green, 10", with the etched birds but no longer any trace of silver. 
This is a smaller vase with the same decor:
In this detail, from another vase, the bird is not covered in silver deposit, but has a green hue:
By this time, I had learned that vases of this type of decoration are commonly attributed to Karl Goldberg, who in 1891 opened a decoration workshop in Arnultovice, near Nový Bor (Truitt 1:44). The earliest examples are found in Pazaurek's 1901 book on modern glass. It is worth mentioning that Pazaurek dedicates a whole chapter to identification of decors by company or artist. In some cases, blanks by one company were decorated by another company or by a particular artist. 
 8. PAZAUREK 1901, 118:126
Vases with acid etched decoration on a yellowish grained surface are found in the Passau Museum Catalog
 9. PMC IV: 259: 456-58
As luck would have it, I found a picture which confirmed the wild bird decoration of my vase as definitely Goldberg: 
 10.  PAZAUREK 1901,  115;118
I think I can now elucidate the mystery of the "fake Loetz signature" on my vase. In order to do so I must introduce a new concept, dual attribution: Pieces of glass in which two companies, or a company and a decorating artist, collaborated. One provided the blank, another the decoration.
Heckert pieces, for example, are signed both by Max Rade, the decorating artist, and Fritz Heckert, the glass maker. I have recently received correspondence on the fact that a number of Harrach pieces are marked with the distinctive Pohl signature. The most revealing section of Truitt 1 (76-77) contains pages from a Hosch catalog showing both Kralik punched handle pieces (commonly but incorrectly attributed to Marie Kirschner) and Loetz three handled pieces (commonly but incorrectly attributed to Michael Powolny).
But my vase is different. In this case, the blank was made by the most prestigious company of the period, and it carried its signature on the bottom. Karl Goldberg took care of the decoration, utilizing what was probably his most beautiful design. The signature is genuine; the decoration is also genuine. It is a Loetz/Goldberg vase. From now on, all research must take dual attribution into account.