Identifying and Cleaning Alabaster Marble and Onyx French Clock Cases

This article focuses on identifying and safely cleaning white stone French clock cases distinguishing alabaster from marble and onyx, covering Mohs hardness scratch test using copper penny (scratches gypsum alabaster hardness 2) versus steel knife (doesn't scratch marble hardness 3 or quartz-based onyx hardness 7), translucency test placing bright LED light inside case where alabaster shows remarkable light transmission while marble remains relatively opaque, understanding that gypsum alabaster (calcium sulfate modern alabaster) is extremely water-soluble requiring acetone-dampened not water-based cleaning while calcite marble (calcium carbonate) tolerates water better, GOJO waterless hand cleaner with toothbrush technique removing surface grime from marble without moisture damage, and Borax slightly-damp cloth method for alabaster followed by Renaissance Wax or cosmolloid museum-grade wax protecting porous surface from future contamination and handling damage.

Understanding white stone composition

Three different white stones

French clock cases from 1800s-early 1900s used three distinct white stones often confused due to similar appearance: Gypsum alabaster (modern alabaster)—calcium sulfate same chemical composition as plaster of Paris, extremely soft (Mohs hardness 2), very translucent almost transparent, highly water-soluble requiring extreme care during cleaning, commonly mined in Tuscany (Volterra region) Mexico and southwestern United States. Calcite marble (true white marble)—calcium carbonate metamorphosed limestone, harder than alabaster (Mohs hardness 3), less translucent than alabaster, reasonably water-resistant allowing careful wet cleaning, and reacts to acid producing carbon dioxide bubbles. Quartz-based onyx (true onyx or Brazilian onyx)—silicon dioxide in banded or variegated colors including white green pink brown, very hard (Mohs hardness 7), virtually impermeable to water, expensive and used in highest-quality French cases. Additionally: Mexican "onyx" is actually calcite alabaster not true onyx, and Castellina "marble" is heat-treated gypsum alabaster not true marble.

Why identification matters critically

Cleaning methods safe for marble or onyx destroy alabaster catastrophically: water-based cleaning on gypsum alabaster dissolves surface creating permanent cloudy appearance ruining original polish, poultices used for marble cleaning literally melt alabaster, excessive moisture causes alabaster to swell crack and disintegrate, and once water damage occurs restoration is essentially impossible. Conversely: cleaning methods safe for alabaster (solvent-based only) are unnecessarily cautious for marble wasting effort. Therefore positive identification before any cleaning attempt is absolutely essential. Treating unknown white stone as if it were alabaster (most fragile option) provides safety margin—solvent cleaning doesn't harm marble or onyx but water cleaning destroys alabaster irreversibly.

Historical context and manufacturing

French clock manufacturers (Japy Frères, Samuel Marti, others) selected stone based on price point and market: High-end cases used Brazilian onyx or finest white marble—expensive durable highly polished appearance, Middle-tier cases used European white marble—good durability reasonable cost adequate polish, Economy cases used gypsum alabaster—cheapest option, soft allowing easy carving and machining, attractive translucency, but fragile requiring protective glass dome. Alabaster cases typically featured brass trim strips along edges (easily drilled for attachment into soft stone) while marble cases rarely had such trim. Clock movements in alabaster cases were predominantly French (Paris manufacturers) as Italian alabaster from Volterra was readily available. Understanding manufacturing economics guides expectations—alabaster case on expensive complicated movement is unlikely while simple time-only movement in alabaster case is typical.

Mohs hardness scratch test identification

Understanding Mohs scale

Mohs hardness scale (established 1820s by Friedrich Mohs) ranks minerals 1-10 by scratch resistance: 1 Talc (softest), 2 Gypsum, 3 Calcite, 4 Fluorite, 5 Apatite, 6 Feldspar, 7 Quartz, 8 Topaz, 9 Corundum (sapphire/ruby), 10 Diamond (hardest natural material). Each mineral scratches all minerals below it on scale. Common objects positioned on scale: Fingernail 2.5, Copper penny 3, Steel knife blade or window glass 5.5, Steel file 6.5. For clock case identification: Gypsum alabaster (hardness 2) scratched easily by fingernail or copper penny, Calcite marble (hardness 3) scratched by steel knife but not copper penny, and Quartz onyx (hardness 7) scratches steel knife not vice versa. This systematic approach provides definitive identification when properly executed.

Performing penny test

Copper penny test distinguishes alabaster from marble: select inconspicuous area on case interior or bottom where scratch won't be visible, use copper penny (not modern zinc-core pennies—use pre-1982 solid copper penny if available though modern pennies still work), press penny edge firmly against stone and draw across surface applying moderate pressure, wipe test area with dry finger removing any copper streak deposited by penny, inspect closely under bright light for actual scratch in stone surface. Results: If penny scratches stone easily creating visible groove—stone is gypsum alabaster (hardness 2 softer than penny hardness 3). If penny leaves copper streak but no scratch in stone—stone is calcite marble or harder (hardness 3+ harder than penny). This simple test performed in 30 seconds provides reliable preliminary identification without expensive equipment or expertise.

Steel knife confirmation test

If penny doesn't scratch stone, steel knife test distinguishes marble from onyx: use steel knife blade (pocket knife, utility knife) on same inconspicuous area, press blade edge against stone with firm pressure drawing across surface, wipe and inspect for scratch. Results: If knife scratches stone—stone is calcite marble (hardness 3 softer than steel 5.5). If knife doesn't scratch stone and stone is white or banded colors—stone is quartz-based onyx (hardness 7 harder than steel). If knife doesn't scratch and stone is mottled gray-black—stone is granite (mixed minerals including quartz). For clock cases: finding that knife doesn't scratch white stone confirms valuable Brazilian onyx case deserving maximum care and professional attention for significant damage. However, most French clock cases are either alabaster or marble—onyx cases are relatively uncommon due to high cost and difficult machining.

Translucency and acid tests

LED light translucency test

Alabaster's characteristic translucency provides visual identification: remove movement from case, place bright LED light (9-bulb or similar compact powerful LED) inside case in darkened room, observe whether light glows through stone walls. Results: Gypsum alabaster glows remarkably—light transmits through inch-thick stone creating lantern-like appearance, internal structures and details become visible, and entire case appears luminous. Calcite marble shows minimal translucency—very thin sections (less than 1/4 inch) may show slight light transmission but thick case walls remain opaque. Quartz onyx shows moderate translucency—some light transmission in thin sections depending on color and purity but less dramatic than alabaster. This non-destructive test requires only flashlight or LED and provides compelling visual evidence. Historical note: alabaster's translucency made it popular for lamp shades and light fixtures—characteristic shared with clock cases.

Acid test for carbonate stones

Acid test distinguishes carbonate stones (marble, calcite alabaster) from non-carbonate (gypsum alabaster, onyx): calcite marble and ancient calcite alabaster both calcium carbonate react with acid releasing carbon dioxide bubbles—characteristic fizzing indicates carbonate, while gypsum alabaster (calcium sulfate) and quartz onyx (silicon dioxide) don't react to acid showing no fizzing. Test procedure: place single drop of weak acid (white vinegar 4% acetic acid, or dilute muriatic acid) on inconspicuous area, observe for bubbling. However, this test has significant drawbacks: acid can etch marble surface leaving permanent dent especially if calcium carbonate content is high, reaction may be slow with vinegar requiring extended observation, and muriatic acid is aggressive potentially causing excessive damage. Therefore: scratch test and translucency test are preferred identification methods—use acid test only when other tests are inconclusive and understand that permanent marking may result. Always test smallest possible area with weakest acid available.

Cleaning alabaster safely

Critical water prohibition

Gypsum alabaster is essentially plaster of Paris (calcium sulfate hemihydrate)—literally the same material used for wall construction and sculpture casting. Water exposure causes: surface dissolution creating permanent cloudy appearance destroying original polish, absorption into porous structure potentially causing swelling and cracking, and conversion of calcium sulfate back toward gypsum (the mineral from which plaster is made) fundamentally altering surface character. Even minimal water contact—damp cloth, humid environment, condensation—damages alabaster progressively. Conservation principle: treat alabaster clock cases exactly like plaster of Paris sculptures because chemically they are identical. Never use: water-based cleaners of any kind, damp cloths or sponges, steam cleaning, or poultices recommended for marble. Alabaster under glass dome historically remained clean because dome protected from dust and handling—cases without dome protection require extreme care during any cleaning intervention.

Acetone cleaning method

Safest alabaster cleaning uses pure acetone (not nail polish remover containing oils and moisturizers): work in well-ventilated area—acetone fumes are harmful and flammable, use cotton swabs (Q-tips) dampened not dripping with pure acetone, gently wipe small area testing effectiveness and observing for any adverse reaction, if safe proceed systematically covering entire surface with fresh acetone-dampened swabs, dirt dissolves in acetone appearing as brown discoloration on swab, continue with fresh swabs until swab emerges relatively clean, let acetone evaporate completely (minutes)—it leaves no residue. This method removes surface grime, oils, and light staining without water contact. For stubborn staining: multiple gentle passes with acetone preferred over aggressive single application. However, understand that deeply penetrated stains (rust, water damage, mineral deposits) may be permanent—acetone removes surface contamination only not stains that have chemically reacted with calcium sulfate or penetrated deeply into porous structure.

Alternative Borax method

Some conservators recommend Borax (sodium borate) for alabaster cleaning as compromise allowing minimal moisture: mix Borax powder with tiny amount water creating thick paste almost dry consistency, apply sparingly to soft cloth—cloth should feel barely damp not wet, gently wipe alabaster surface with minimal pressure, dirt transfers to cloth, immediately wipe with second clean dry cloth removing any residual Borax and moisture, work in small sections ensuring no prolonged moisture contact. This method provides slight additional cleaning power versus pure acetone while minimizing water exposure. However, controversy exists—some conservators reject any water-based method for alabaster as unnecessarily risky. Safest approach: begin with acetone cleaning, proceed to Borax only if acetone proves insufficient, and accept that some staining may be permanent rather than risking water damage attempting impossible stain removal.

Cleaning marble safely

GOJO waterless hand cleaner technique

GOJO waterless hand cleaner (without pumice—pumice version is abrasive) effectively cleans white marble cases: apply GOJO directly to marble surface or to soft cloth, use old toothbrush working cleaner into carved details and recesses where dirt accumulates, dissolved grime appears as dark discoloration in cleaner, wipe away dissolved contamination with clean cloth, repeat application until cloth emerges relatively clean, and final wipe with clean dry cloth. GOJO advantages: petroleum-based formula doesn't contain water avoiding grain-raising or staining concerns, gentle enough for delicate stone surfaces, effectively dissolves oils fingerprints and organic contamination, and readily available from hardware stores and janitorial suppliers. This method produces dramatic improvement on grimy marble cases revealing clean white stone underneath decades of accumulated dirt. For extremely dirty cases: preliminary cleaning with mineral spirits or paint thinner may be appropriate removing bulk contamination before GOJO final cleaning.

Traditional marble cleaning approaches

Professional marble conservation uses water-based poultices but these require expertise and appropriate equipment: poultice (absorbent material saturated with water or chemical solution) is applied to stained area, covered with plastic preventing evaporation, left for extended period (hours to days) drawing stains from stone, then removed and stone rinsed. This technique effectively removes deep stains but risks: over-wetting causing water staining or mineral deposits, incomplete drying promoting mold growth in humid environments, and damage to fragile thin sections through moisture expansion. For amateur clock case cleaning: GOJO waterless method provides excellent results without water-based poultice risks. Reserve poultice cleaning for professional conservators treating severely stained valuable cases where water-free methods prove inadequate. Most marble clock cases respond well to gentle solvent cleaning making elaborate wet methods unnecessary.

Paste wax protection after cleaning

After cleaning marble or alabaster, protective wax coating prevents future contamination: Renaissance Wax (museum conservation standard, expensive but excellent), Butcher's Bowling Alley Wax (high carnauba content, good quality, more affordable), or cosmolloid wax (museum-grade microcrystalline wax used by professional conservators). Application: ensure stone is completely clean and dry, apply thin coat of paste wax with soft cloth, let dry until hazy (15-30 minutes), buff with clean soft cloth achieving subtle sheen, and repeat applying 2-3 thin coats for maximum protection. Wax fills microscopic pores reducing dirt accumulation, provides slight water resistance (though not sufficient for wet cleaning), enhances color and figure of stone, and creates smooth surface facilitating future dusting. Waxed surfaces require only occasional dusting with soft cloth maintaining clean appearance indefinitely. Reapply wax every few years as needed when surface appears dull or contaminated.

Special considerations and damage

Typical alabaster deterioration

Alabaster's softness and fragility create characteristic damage patterns: edge chips and corner losses from handling impacts, surface scratches from careless cleaning or abrasive contact, cracks from structural stress or impact, powdery surface degradation from moisture exposure or poor storage, and discoloration from rust (metal hardware contact), water staining, or absorbed oils. Some damage is repairable: small chips can be filled using alabaster powder mixed with appropriate binder creating color-matched fill, surface scratches may be reduced through careful repolishing with fine abrasive though original factory polish cannot be fully restored, and discoloration sometimes lightens with proper cleaning. However, extensive damage (large cracks, severe water damage, structural failures) may be beyond amateur repair requiring professional conservation or acceptance of damaged condition. Alabaster's value is primarily aesthetic—damaged piece has significantly reduced display value but retains historical interest and movement may be perfectly functional.

Brass trim preservation

Alabaster cases typically feature brass trim strips along edges attached through soft stone into wooden backing: never forcibly remove brass trim—alabaster is too fragile for aggressive disassembly, clean brass in place using appropriate metal polish and soft cloth, if brass must be removed for dial restoration proceed with extreme caution noting exact attachment method, screws through alabaster into wood backing are common—remove slowly preventing alabaster cracking, and replace carefully using original screw holes avoiding new drilling which may crack stone. Brass trim serves multiple functions: protects vulnerable alabaster edges from chips, conceals joints between stone sections, and provides decorative accent complementing white stone. Tarnished brass on white alabaster appears neglected—polished brass dramatically improves overall appearance making cleaning effort worthwhile.

FAQs

How do I tell if my white clock case is alabaster or marble?

Scratch test: copper penny easily scratches alabaster but not marble. Translucency test: place bright LED inside case—alabaster glows remarkably, marble remains opaque. These two tests provide definitive identification without expensive equipment. Additionally: alabaster typically has brass trim strips on edges, marble cases rarely have such trim. Alabaster is much softer and more fragile than marble requiring extreme care during handling and cleaning.

Can I clean alabaster clock case with water?

Absolutely not. Gypsum alabaster (modern alabaster, calcium sulfate) is water-soluble like plaster of Paris. Water exposure dissolves surface creating permanent cloudy appearance ruining original polish. Even damp cloth causes damage. Use only acetone-dampened cotton swabs or Borax thick paste barely-damp cloth for cleaning. Treat alabaster exactly like plaster sculpture—no water contact ever. This is most critical rule for alabaster care.

What is GOJO and why use it for marble cleaning?

GOJO waterless hand cleaner (without pumice) is petroleum-based cleaner effectively removing dirt, oils, and fingerprints from marble without water. Apply with cloth or toothbrush, work into details, wipe clean. Advantages: no water avoiding staining risks, gentle enough for delicate surfaces, readily available, and produces excellent results. Use GOJO version without pumice—pumice is abrasive and may scratch polished marble. For marble cases, GOJO provides professional-quality cleaning without specialized equipment.

How do I protect alabaster or marble after cleaning?

Apply 2-3 thin coats museum-grade paste wax: Renaissance Wax (expensive, museum standard), Butcher's Bowling Alley Wax (good quality, affordable), or cosmolloid wax (professional conservator choice). Apply thin coat with soft cloth, let haze, buff, repeat. Wax fills microscopic pores preventing dirt accumulation, provides slight moisture resistance, and enhances stone appearance. Reapply every few years when surface appears dull. Waxed surface requires only occasional dusting maintaining clean appearance.

What is difference between gypsum alabaster and calcite alabaster?

Gypsum alabaster (modern alabaster, calcium sulfate)—extremely soft (hardness 2), very translucent, highly water-soluble, common in 19th-20th century clock cases. Calcite alabaster (ancient alabaster, calcium carbonate)—slightly harder (hardness 3), translucent, reasonably water-resistant, rare in clock cases. Most white clock cases are either gypsum alabaster or calcite marble—both require careful identification before cleaning. Safest approach: treat any white translucent case as gypsum alabaster avoiding all water contact.

Can deep stains be removed from alabaster?

Depends on stain type and depth. Surface contamination (dirt, oils, light staining) removes with acetone or Borax cleaning. However, deeply penetrated stains (rust from metal contact, water damage minerals, absorbed oils) may be permanent—acetone removes only surface contamination not stains chemically bonded to calcium sulfate or deeply absorbed into porous structure. Attempting aggressive stain removal risks additional damage. Accept that some historical staining may be permanent rather than risking alabaster destruction pursuing impossible perfection.

Is Brazilian onyx really onyx or different material?

True Brazilian onyx is quartz-based (silicon dioxide, hardness 7)—extremely hard, virtually impermeable, available in multiple colors including white green pink brown, and very expensive. This is genuine onyx, not misnomer. However, Mexican "onyx" is actually calcite alabaster not quartz—much softer and requires different care. Brazilian onyx French clock cases are relatively rare due to high cost and difficult machining. Most white French cases are alabaster or marble, not true onyx. Scratch test confirms: knife cannot scratch true onyx.