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  1. #1
    Registered User RobertG's Avatar
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    Default Marble, white alabaster or onyx

    Since the thread on slate vs black marble has been so interesting and educational, below are three clocks that I have that I need to identify the stone from which they are made before I try any kind of cleaning action.

    I have read that alabaster is actually quite rare and very soft, absorbent, and delicate; marble is much easier to clean, and I have found nothing on white onyx or how to clean it.

    How can one tell the difference between the stones?

    So, what are your ideas as to the composition of these clocks? I photographed them at night using a flash, but if daylight will help, I will try to retake and repost them using natural light.

    What do all ye say?
    Attached Thumbnails Attached Thumbnails DSCN0274.jpg   DSCN0279.jpg   DSCN0280.jpg   DSCN0281.jpg  

  2. #2
    Forums Administrator harold bain's Avatar
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    Default Re: Marble, white alabaster or onyx (RE: RobertG)

    Nice clocks, Robert, and great topic. The pictures are of my Emile Farcot white marble clock (before and after). I just used a waterless hand cleaner and a tooth brush, and was afraid to use anything stronger, suspecting that the wrong chemical would drive the stains deeper. Perhaps someone will have a better idea
    Attached Thumbnails Attached Thumbnails 100_0332.jpg   100_0335.jpg  
    harold bain, Member ch 33
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  3. #3
    Registered User RobertG's Avatar
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    Default Re: Marble, white alabaster or onyx (RE: harold bain)

    Nice clocks Harold. Your work really improved the appearance.

    I have been afraid to try anything on mine until I know more about the stone. I have read that alabaster absorbs any liquid and is dissolved easily by water. I don't want to risk anything until I know more.

    From what I have read about alabaster, it is so fragile that even museums dislike owning it. I doubt seriously if clocks were ever made of something so delicate, but that is what I want to know.

    I am hoping one of the geologists and/or rock hounds out there will tell us more.

    RobertG

  4. #4

    Default Re: Marble, white alabaster or onyx (RE: RobertG)

    I'm neither geologist nor rock hound, but marble is metamorphosed limestone and as such it will react to acid by releasing bubbles of carbon dioxide. If you put a drop of weak acid on marble, it will fizz. I'm not sure that vinegar always works, but you might be able to find muriatic acid (hydrochloric acid) at the hardware store. Onyx is quartz-based and will not react to acid.

    I'm less sure about alabaster, but I think it is unlikely to have been used for a clock case, as it is quite soft.
    Jeremy

  5. #5
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    Default Re: Marble, white alabaster or onyx (RE: Jeremy Woodoff)

    Actually, alabaster is quite common in French clocks, and looking at your's Robert, I'm inclined to say that they are alabaster. If you can easily scratch the stone with a pin, then you can be certain. Harold’s white marble would be fairly resistant to a pin.

    The damage on one of your clocks, is quite typical to alabaster cases. Also, alabaster is quite a lot more translucent than plain white marble. Large dish shaped light bowls for overhead lights are quite common, because of that.
    -> posts merged by system <-
    alabaster shade:
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  6. #6
    Registered User RobertG's Avatar
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    Default Re: Marble, white alabaster or onyx (RE: laprade)

    Thank you.

    So how does one go about cleaning these clocks, especially the alabaster?

    RobertG
    Last edited by RobertG; 09-16-2009 at 10:19 AM. Reason: Entire sentence was missing upon posting

  7. #7
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    Default Re: Marble, white alabaster or onyx (RE: RobertG)

    Robert, I don't know how to clean alabaster. Try speaking to the conservators in the sculpture section of a "good" art gallery, preferably a government one.

    I have never had to clean it, and can’t even give an educated guess.

    A better picture of alabaster in horological use!
    Attached Thumbnails Attached Thumbnails alabaster dial.jpg  

  8. #8
    Registered User RobertG's Avatar
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    Default Re: Marble, white alabaster or onyx (RE: laprade)

    There are two websites about cleaning alabaster that I have found:

    http://www.ehow.com/how_2302442_clean-alabaster-.html

    and

    http://www.buildingconservation.com/.../alabaster.htm

    Both are very interesting.

    RobertG

  9. #9

    Default Re: Marble, white alabaster or onyx (RE: RobertG)

    Thanks, Robert, for posting those sites. The building conservation website was especially interesting (I love those Regency "cantilevered" stone stairways!).
    Sigh.... About these white stones.....
    I almost hesitate to talk about this subject, because the terminology is so confusing, but here goes....
    Alabaster (in addition to being a word used for anything white) can really be either of two stones. Both types are white and translucent, and are even used for window panes.
    1. Ancient alabaster, as used for ancient Egyption perfume jars, is calcite, calcium carbonate, chemically the same as limestone, marble, chalk (but not blackboard chalk- that's gypsum!) or marble. Classically it's pure white, and quite translucent, even transparent. It gives a positve acid test (bubbles with HCl) and is quite soft, but is reasonably resistant to water. It's still mined in Egypt and Algeria.
    2. Modern alabaster (which is what is usually meant nowadays) is, chemically, calcium sulphate, or gypsum, AKA plaster of Paris. This is even softer than calcite alabaster, gives a negative acid test, and is somwhat soluble in water (which can be a real problem in cleaning- even a slight wetting can ruin the polish.) Like calcite alabaster, it is very translucent, even transparent. It is not rare, being found in Mexica, the SW US, Pakistan, China (isn't everything?) but is especially known from Tuscany, particularly Volterra, where the hill under the city has been, from the time of the Etruscans, (at least) completely honeycombed by mines for it. In that town, there is an alabaster museum, which has, probably, hundreds of clocks from the 19thC, usually with French movements, like yours (as well as a gift shop selling alabaster items which clearly show how far the art of alabaster carving has sunk since then!).
    But this nomenclature is way too simple.... The Tuscans also treat their alabaster in hot water, which eventually would change the crystal structure into something like the interior of drywall board- but they stop it partway, and the result looks very much like real marble. This they call Castellina marble, after the city where this is done, or just marble. Being much softer than real marble, it's much easier to carve, and thus cheaper. It's commonly sold to tourists in Florence.
    In addition, Mexican calcite alabaster is called "onyx" (although real onyx is quartz, silicon dioxide, a hard stone) or "onyx marble", or just "marble". This is found near Puebla in a characteristic green color, but also in shades of reddish brown, both frequently banded or striated. It's also used for clock cases (usually with American movements, or "lite French" movements).
    Although Harold's case looks like real marble, his cleaning method sounds good to me: no water! (Although I must warn that I have absolutely no practical experience with it.) The method historically, and scientifically, used for cleaning real marble, i.e. water based poultices, would be disastrous for gypsum alabaster, as well as for Castellina "marble".
    Treat these cases like they're made of plaster of Paris, because, chemically, they are.
    Last edited by Bill Ward; 09-19-2009 at 12:31 AM.

  10. #10
    Principal Administrator John Hubby's Avatar
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    Default Re: Marble, white alabaster or onyx (RE: Bill Ward)

    Bill, I'm wondering if the difference in composition is why Brazilian onyx is highly preferred over Mexican "onyx" for clock cases. The very best French cases of the 19th and early 20th century were advertised as "Brazilian Onyx" and from my observation the stone is quite hard, virtually impermeable to water, and has all the appearance of Brazilian quartz gemstones when highly polished. I have seen Brazilian onyx in multiple colors such as green, pink, white, orange, browns, and variegated; the most popular being green varieties followed by white. The variegated stone usually is green with white, red, or ocher color inclusions and striations, but I've also seen white onyx with reddish brown color segments as well and brown with white inclusions.

    I have a friend in São Paulo who is a jeweler and gemologist, has family owned properties in the state of Minas Gerais where they mine all sort of precious and semi-precious stones but also mine onyx; it was from seeing the multiple varieties of onyx at his shop that I learned what was available there.
    Last edited by John Hubby; 09-19-2009 at 12:43 AM.

  11. #11
    Registered User RobertG's Avatar
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    Talking Re: Marble, white alabaster or onyx (RE: Bill Ward)

    Quote Originally Posted by Bill Ward View Post
    Thanks, Robert, for posting those sites.).
    Sigh.... About these white stones.....
    I almost hesitate to talk about this subject, because the terminology is so confusing, but here goes....
    Well, that clears that up!

    Thank you for the information. I knew going into this topic, it was going to be confusing. I guess the safest approach would be that recommended in one of the referenced sites: trying the acid test, then using an acetone dampened (not saturated) Q-tip--NO WATER. Followed by the application of the recommended wax; which can be purchased from this site (along with other items appropriate for clock restoration):

    http://www.talasonline.com/

    Cleaning these clocks will be very labor intensive.

    Thank you, everyone for your help.


    RobertG

    PS: I don't know why that website link isn't live.

  12. #12
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    Default Re: Marble, white alabaster or onyx (RE: RobertG)

    Bill, Robert, Harold

    The alabaster cases were usually under glass, which helped to keep them clean. Most alabasters, that I have seen, were without glass bezels and thus, under a dome.

    Talking about "soft stone" and cantilevers:

    There is an amazing staircase in the former monastery (17th c), now the Mairie, at Brantôme in the Dordogne, known as the “Venice of the Dordogne”. The staircase is in “french fossil” limestone, which is a very soft stone, and prone to having hidden lumps of silicate in it.
    (I went over to look at the large clock they have in one of the towers. They let you in to look at the workings, but the custodian was off sick!. I’ll be posting some pictures in the Monumental section soon. (you will see the cantilevered staircase)


    Harold, your white marble is quite nice. They aren’t very common: I only ever handled three! I think the standard type weren’t very popular, because it was difficult to keep them clean: finger grease and household grime etc. The ones that I handled, two were under glass, with no bezels, and one was same as yours, with a bronzed lion on top.

    I must admit, to not liking "onyx" clocks very much. The cases never seemed to be very well designed. I suppose it is to do with the hardness and structure of the stone, which would make machining difficult.

  13. #13
    Registered User RobertG's Avatar
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    Default Re: Marble, white alabaster or onyx (RE: laprade)

    Quote Originally Posted by laprade View Post
    The ones that I handled, two were under glass, with no bezels, and one was same as yours, with a bronzed lion on top.
    Laprade:

    I assume, from your description, that my clock shown on the far left of the first posting in this thread (with the almost non-existent dial) would be a white marble, like Harold's. It has a hole in the top for some missing part, maybe a lion?

    Harold:

    How is the lion affixed to your clock? Mine has a hole for a bolt to run through the case, and it has a wider shoulder that sits into a recess.

    RobertG

  14. #14
    Forums Administrator harold bain's Avatar
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    Default Re: Marble, white alabaster or onyx (RE: RobertG)

    No lion on mine, Robert, but any I have seen with ornamentation had holes through the case, and nuts on the inside.
    harold bain, Member ch 33
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    Default Re: Marble, white alabaster or onyx (RE: harold bain)

    Lads,

    Generally speaking, clocks with a single hole on the top, usually had an urn or a "tazza", on top. Robert, I suspect, that one of your clocks is missing its "tazza".

    Figurines and animals, usually have two holes.

    Robert, you mention the "first" picture. Only the face is shown, and from what I can tell, it looks to be alabaster. It was more common for alabasters to have brass / gilt trim, as drilling the fixing holes was relatively easy, than "marble" models.

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