Carbon Filament with Iced Glass Bulb
During the 1890s The Edison-Swan United Electric Lamp Company excelled in the manufacture of so-called Fancy lamps, and offered a range of several dozen different types each having some feature of decorative value. Among the most intriguing both for their appearance as well as the skill required in their manufacture is the Iced Glass model. The broken glass surface causes multiple refraction of the light and a highly attractive effect when illuminated.

The description accompanying these types in a 1930s guide book to the Ediswan Collection of Historic Lamps gives an insight into how they were produced. The crazed surface was achieved by forming a bulb with unusually heavy wall thickness, and plunging the still red-hot glass into water immediately after blowing. Such rapid cooling creates high thermal stresses, the effect of which was to split the surface of the glass. The majority of bulbs shattered instantly but with skilful handling a small proportion survived the treatment. As an example of the thickness of the glass, the capless versions of this lamp having platinum loop terminals turn the scales at 4¾ ounces (135g), whereas a clear lamp of the same size and shape weighs only ½ oz. (14g)

The rest of the construction of this lamp is similar to ordinary types of its era, having platinum lead wires pinched directly into the neck of the bulb. The filament is secured with a deposited joint of carbon. The bayonet cap is made from standard pipefitters' 7/8" (22mm) brass tubing with plaster of paris insulation. In view of the very high list price of these lamps it is unlikely that few, if any, were sold. The only known examples are in the Ediswan Collection and with private collectors whose lamps originated from the same.
Manufacturer: The Edison-Swan United Electric Light Co. Ltd.
Lamp Power: Approx 60 Watts
Lamp Voltage: 100 Volts
Lamp Current: 0.6 Amperes
Cap Type: B22d Brass + Plaster of Paris
Bulb Type: P-57t P-18t in eighths/inch
Bulb Finish: Iced Amber Soda-lime glass
Filament Type: Squirted Carbon
Atmosphere: Vacuum
Luminous Flux:
Luminous Efficacy:
Beam Intensity: N/A
Beam Distribution: N/A
Colour Temperature & CRI: CCT: CRI:
Chromaticity Co-ordinates: CCx: CCy:
Rated Lifetime: Approx. 800h
Burning Position: Universal
Overall Length: 100 mm 4 inches
Light Centre Length:
Factory: Ponders End England
Date of Manufacture: c.1895
Original / Present Value: 6s9d (1896) £30.76 (2011)
 
 
References: 1) Catalogue of the Edison & Swan United Electric Lamp Co. Ltd., 1893
2) Catalogue of the Edison & Swan United Electric Lamp Co. Ltd., 1896
3) Catalogue of Exhibits of the Ediswan Collection of Historic Lamps, c. 1930