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"slag" Vs. "onyx"


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These are comments found in Bob's recent white slag thread.

I believe I am seeing all slag/onyx marbles here. Could be wrong, certainly have been before. My understanding is a Striped Transparent will have a transparent base glass with an opaque color(s) other than white. If it is only transparent and white, it's a slag.


I agree with 1Dans above. I don't think collectors agree on nomenclature, though. I do know 1)that striped transparents seem to always sell for more money than slags and 2) the term "onyx" rarely gets used even though it should be.

Please elaborate on the appropriate usage of the term "onyx" in connection with slags. (I understand it is also the name of an Akro corkscrew.)

Okay ... when I went to double check on the usage of "onyx" in connection with corks, I stumbled onto a partial answer to my question. In addition to confirmation that Onyx was an official corkscrew name, the Akro page at Marblealan.com says this about slags:

Akro Agate slags ("Striped Onyxes") were available in the following colors (in increasing order of rarity): amber, purple, blue, green, red, aqua, clear, vaseline, and orange. The red slags were called Cardinal Reds by the company. Like the slags of other companies, those of Akro were produced by the single-stream method and include a transparent colored based mixed with opaque white glass. One exception is the Cornelian which was produced in the same method as a slag but consists of an opaque red base mixed with opaque white.

(i.e., except in a couple of special cases, Akro Agate slags would have been known as onyxes in their day?)

Next on the MFC page I found this:

Slags were called National Onyx by the company and were available in such colors as amber, purple, blue, green, clear, aqua, yellow, orange, and lavender, in approximate increasing order of rarity. This company did not produce red slags as earlier thought. Very dark blue slags were coined "Royal Blues." Some slags were produced in very large (over 1 1/2") sizes.

Some National Onyxes, which are probably early types, are referred to as "horizontal slags." These are easily recognized, as instead of having a single "nine" swirl the white spirals multiple times around the marble, forming a tight corkscrew pattern. These are valued much more highly than regular slags.

There was one additional type of slag marble produced by M.F. Christensen. These are oxblood slags (possibly called "moss agates" by the company), which have a very dark transparent green base and an oxblood swirl. These are uncommon.

And on the Peltier page:

Peltier slags were called National Onyx by the company and were available in colors of brown, blue, green, aqua, purple, red, and yellow, in approximate increasing order of rarity.

The other reference I find to "onyx" at MarbleAlan.com is on the non-glass handmade marbles page:

.... onyx agates are black, and striped onyx agates have alternating black and white bands.

(so the white bands on the natural onyx marble are the inspiration for the name "onyx" in connection with slags?)

Now, when I thought I almost had it figured out, I'm not finding any reference to "onyx" on Marblelan's CAC page.

What did Christensen call their slags?

Is it known/believed that with a few exceptions such as the Cardinal Reds noted above, the common name for all slags in the early 1900's would have been "onyx"?

If so, was the name supplanted in the minds of the populace by Akro's usage of it in connection with their corkscrews? Or is it your feeling that the shift occurred later?

Thank you very much!


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I believe the companies used the term onyx for thier marbles which were meant to imitate the hand cut/ground agate types from Germany. Akro also used Carnelian for the same reason. Some of the ones from Germany were made from onyx and carnelian stone.

Striped Onyx.


Of course the original, German, handmade slags did not have a name that I am aware of.

Clear as mud, right?


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Awesome box, Dan. In case anyone missed the name on it (and to put it into searchable text form!), the label includes the lines:



(I love that they feel they have to make it clear the marbles are toys!)

I guess Akro used the name "onyx" for the corks because it was a naturally descriptive adjective, not to steal a common marble name and make it their own brand name. No way of knowing for sure, I s'pose.

The gist of what I'm hearing about the term onyx in connection with slags boils down to this: in the 1910's through 1930's if an American schoolkid was shown a slag, and asked what kind of marble it was, he'd say it was an onyx.

does that sound about right?

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