Black, Ebony, Hyalith, Oh My

[ann]

Picking up from another thread, I thought it might be interesting to start a topic that came up along the way . . .

I think that most of us have learned that there is no truly black glass -- it's generally a very dark purple, or blue, or, less commonly, green. I know that it is occasionally possible to tell what "color" the black really is (when even a tiny bit flows over or under white), and I've seen that on my own marbles.

However, long ago and far away I was a geology major (for 2 half-forgotten semesters), and therefore I know that there is a naturally-occuring black glass called obsidian. Once lava. If anyone here has held a flaked obsidian blade and stared hard at the vaunted sharp edge (surgeons use it today) you've seen that it's black. Where it thins, it thins into grayness, And yes, of course I tried it out. Stupid move. Way worse than a paper cut.

And then I got a copy of the recently-published batch book that belonged to Henry Hellmers, Akro's glass chemist in the 1920s and again in the early 30s (he was lured away by Cambridge Glass for awhile). He recorded 37 formulae for black / ebony/ hyalith glass, including 5 old German ones and four for Cambridge Glass.

I copied out three of them -- two from Akro Agate and one he developed for Alley Agate, because you can see his tweaking with both the chemicals and the amounts.

For Akro Agate, what he called "pot" glass, used for striping as opposed to a base color ("tank" glass), he did two batches on 5/13/28, each of which he called "Black Opal." His notes say "Dense, good."

All measurements are in pounds.

Formula #1

sand 1000

soda 360

nitrate 40

manganese dioxide 25

cobalt 1 1/4

feldspar 250

fluorospar 110

sodium fluorosilicate 40

Potassium bichromate 5

nickel oxide 2 1/2

Formula #2

sand 1000

soda 360

nitrate 37 1/2

manganese dioxide 25

cobalt 1 7/8

feldspar 300

fluorospar 102

sodium fluorosilicate 50

potassium bichromate 6 1/4

nickel oxide 2 1/2

On 10/2/32 he made this batch for Lawrence Alley at Lawrence Glass Co., with the note "for toy marbles"

sand 600

soda 300

limestone 60

coal 30

manganese dioxide 80

cobalt 1/2

potassium bichromate 7

sulfur 5

I'll leave you with a few more things to keep in mind while pondering.

When speaking of pigment, black is the combination of all colors, while white is the absence of all of them.

[When speaking of light, black is the absence of all colors, and white is the combination of all of them.]

If you have something you've made a very, very dark purple (with manganese, say), and add other things to make it dense and completely opaque -- to seem to the eye to be black (like some Indians, for example) . . . isn't it black?

What do you think?

[Steph]

I think I'd say what I'd learned was not that there is no truly black glass, but that most of what we call black isn't really. For instance, a Marble King bumblebee with purple ribbons. We just naturally call them black -- confusing new collectors along the way.

There's some Akro which seems totally black to me. If it's really something else, I don't know it yet. I'll gladly keep calling it black.

[zaboo]

ahh and there enters the argument about a black popeye. seen many sold on ebay as black when in fact they were not a true black. that said, a real black popeye has dense truly black glass!

I love your research Ann! and we have obsidian examples in our rock garden. yes sharp as a scalpel if you're not careful!

Finding handmade antique marbles with a true black is not an easy do! I have sold 2 in the last year, one on ebay and one privately. The buyers loved them, and were thrilled to get a true black in a handmade. food for thought when on 'the hunt'.

[lstmmrbls]

CAC used about 5 different types of glass that appear black. One of them is black.

[William Marbles]

http://www.cambridgeglass.org/articles/0104/02crystalball350b.php

Found this on the net.... little background on the man.

[akronmarbles]

Formula #1 and #2 contain opacifiers

The last formula from Alley is a highly doped amber / purple / blue / green glass

This makes the base glass:

sand 600

soda 300

limestone 60

This makes amber:

coal 30

Sulfur 5

This makes purpe:

manganese dioxide 80

This makes blue:

cobalt 1/2

And this makes green:

potassium bichromate 7

[ann]

Hi Akronmarbles -- I'd hoped you'd come in. I think what you've told us is very much relevant to the "mixing all colors together makes black," if you're talking about materials (as opposed to light). And thanks for reminding me Dani, I forgot about my few antique Germans with black. They're very, very black.

Not that I intend to argue the point either way. Just that over time I've come to understand that occasionally you'll find a real black. But it was cheaper to just make a very dark purple or a very dark blue or green, so that's what you're usually seeing.

[akronmarbles]

No single element will make 'black' coloured glass. Mixes of colorants are generally used depending on the application of the glass.

Formula #1

glass...

sand 1000

soda 360

nitrate 40

feldspar 250

purple...

manganese dioxide 25

blue...

cobalt 1 1/4

opacifiers....

fluorospar 110

sodium fluorosilicate 40

green....

Potassium bichromate 5

grey...

nickel oxide 2 1/2

Formula #2

glass...

sand 1000

soda 360

nitrate 37 1/2

feldspar 300

purple...

manganese dioxide 25

blue...

cobalt 1 7/8

opacifiers...

fluorospar 102

sodium fluorosilicate 50

green...

potassium bichromate 6 1/4

gray....

nickel oxide 2 1/2

[ann]

Exactly. And some are so dark and dense they have every appearance and characteristic of black. They might as well be black, and some may in truth be black, meeting all of the requirements for it . . .