Opaque and semi-opaque
Below are two photos of a
Persian blue Lotus & Grape bowl (Fenton) taken on a frosty day in
England The shot on the right shows the translucency of the base colour.
First let’s understand exactly
what milk glass, custard glass and moonstone are.
Milk Glass: an opaque white glass, but milk glass collectors use the term to include blue, pink
etc as long as it is opaque. For our purposes in Carnival we usually take it to be the white version but blue milk
glass is also known iridised. Often used tin oxide to make it opaque. Apply iridescence to
milk glass and you get:
- Marigold on milk
- Pearl, that is pastel
iridescence on milk glass
- Iridised blue milk glass
- Smoke iridescence on milk glass.
Detail from a Westmoreland File and Fan comport in
marigold on milk glass. It is shown upside down, and the opaque milk glass is showing under the
Eda Tusenskona (aka
Floral Sunburst) rose bowl in pearl (a very light, pastel iridescence)
Custard Glass: as the
name implies, is more yellowish than milky, and it is opaque. Uranium was added as a colorant to make it pale
yellow and so it GLOWS under UV light. A black light (UV) test will show the difference between milk glass (no
glow) and custard (glow). Apply iridescence to custard glass and you get:
Marigold on custard
- Pearlised Custard – a pastel iridescence
imagine a glass of clear water…now drizzle in a very tiny bit of milk. That’s like moonstone, it is
translucent, not opaque. Moonstone can be clear or blue. Apply
iridescence to moonstone
glass and you get:
- Marigold on
- Pastel iridescence on moonstone
- Persian blue - iridised blue moonstone (can have marigold/bronze
or pastel iridescence).
Slag glass has mixed colours and streaky looking base glass – it’s possible to find base glass with the odd streak
of other colours in it, but true slag is very distinct and is a mixture of a lighter opaque shade (white) plus
another colour, such as:
- Sorbini is the name for Northwood’s blue and white slag
- Caramel / brown and white slag from Riihimaki.
Pictured here are two
Riihimaki Starburst nut bowls - the one on the left is caramel slag (the only one known to date), and on the
right is one in marigold on milk glass. The lower image in both cases shows the base glass of the bowl above it,
clearly demonstrating the difference between the two base glass colours.