Rock - what's behind the term?

A (not overly) short explanation regarding the stone I use.


Alabaster

is - from a chemical point of view - plaster and is found in big nodules in the ground soil where, in prehistorical times, ocean became seas which then completely evaporated. What was left were scale deposits (or in other words: plaster) and as such Alabaster is water soluble and, unfortunately, not immune to frost. That is the reason why, for any lengthy time, Alabaster sculptures feel "at home" only indoors - at home.

 

As for the looks of it, white Alabaster can be confused with Marble, but the former is significantly softer (Mohs hardness 1.5 to 2) and is distinctly warmer to the touch than Marble because Alabaster is a less efficient heat conductor and does not dissolve body heat as quick as Marble.

Alabaster can be worked quite pleasantly, if one keeps in mind its fragility and solubility which are caused by the layering of the stone. Alabaster can be "caressed" into the desired shape with forged hand tools (punch, chisel, rasp) and it responds to sanding and polishing very well. However, Alabaster raises quite some dust when sanding it (water soluble -> sand with only very little water!) and thus Alabaster dust will sit in every crack and cranny of your studio.

 

The award of all this is that Alabaster can be sanded down very thin and - especially the harder variants - will then be quite translucent to a degree close to opal glass. The effects the light plays in these pieces are fascinating every time anew...

 

Alabaster shows some colour variations, from white through honey- and caramel shades right to a chocolate-coloured blackish brown. Additionally, if Lady Luck is on your side, you can find rose- and bluish tinted variations.


"True" Alabaster is used since the old Roman epoch.


There is a namesake "Egyptian Alabaster" which looks like the (plaster) Alabaster but behind that one is more than meets the eye. It is a limestone, considerably harder and non-soluble in water. The reason this "cousin" is - wrongly - named Alabaster roots in its geographical origin: in the old Egypt empire this stone was won in a region with the name "Alabastrites", located in the southern lower Nile valley. The correct name for this "Egyptian Alabaster" would be "Onyx Marble".


Blue Limestone

is the name given in Germany for varied rock. "Irish Blue Limestone" or "Irish Limestone"  as well as a Limestone from the Aachen area are lumped together under that name and additionally a Belgian Slate variety known as "Rechter Blaustein" named after the location Recht in East Belgium and another Limestone from Belgium which is called "Belgian Granite" to confuse people even more.

I shall disregard the Slater here altogether and concentrate on the Limestone variations.

 

What they all have in common is a greyish-blue to antracite colour (greyish-blue when not weathered, black when polished) and the hardness of approximately 3.5 according to Mohs. This hardness puts them next to the harder Marble sorts when it comes to working with them.

The "daily usage" of Blue Limestone is related to that of Marble, too: church walls and facades, some of the more important mundane buildings (town halls etc.) and interior hard-to-wear things like floors, stairs and wash basins, to name only a few of the more important.

And for sculpting, of course...

 

Different than Marble, Blue Limestone shows less veins and layering but more small, light-coloured dots and spots which, if seen from close up, present themselves as fragments of fossile clam shells. This makes the stone a bit more "lively" when polished.

 

As the Blue Limestone is rather hard and with a fine crystal structure but does not tend to brittleness, one can work it rather well with hand tools. Carbide punches and chisels as well as tungsten carbide studded rasps are the choice and when sanding, use a good quality of wet-and-dry diamond spar - this is the way to achieve a wonderfully smooth and hand-charming surface if you are patient and persistant enough.


Kisii stone

sometimes called "Kisii Soapstone", originates from Kisii-Distrikt in West-Kenia, near lake Victoria. The softer varieties of this stone can indeed be worked with woodcarving tools, just like Soapstone, while the harder variants are better worked with simple, forged chisels.

 

Kisii-Stone is generally cream coloured but sometimes bears gifts in the shape of reddish-brown to purple embedded veins and layers. Sometimes you find cracks in the stone which happily house some iron oxide (ordinary rust). At these cracks the stone is prone to split because iron oxide requires significantly more room than the pure iron particles that were sluiced in there. As the saying goes: "one millimeter of iron gives ten millimeters rust".

 

Kisii-Stone varies from about 1 to 2 according to Mohs, that is from "a finger nail marks it" to "a steel nail marks it". Kisii is not prone to crumbling which makes even the harder variants very relaxed to be worked with and a very very smooth surface can be achieved with good wet-and-dry sanding paper.


Marble

is the undisputed classic material when stone sculpting and stone sculptures are mentioned. Seen from a chemical point of view, Marble is a Limestone which decided to take a longn long break some way down the conversion into a carbon dioxide salt, which decision makes a lot of people happy - not just me!

 

Marble as used in sculpting can show basically all colours and come from all over Europe: white Statuario or Paonazzo from Italy (Carrara!), rose coloured Aurora, rose-grau layered Estremoz from Portugal, green Kittilä from Finland, honeycolored Marble from Siena, purple Parnon frpm Greece, black Marmor from Asia Minor - one could carry on and on. And not just the colour but being banded or not, layered or not and the variations of this is close to infinite.

 

Marble is cold - at least it feels cold to the touch - because it is a very good heat conductor and takes the heat off the touching skin rather rapidly. Sometimes the term "cold" is used in an optical sense of the meaning because especially the pure white variants (which are interestingly enough regarded as the most "noble" sorts) give the appearance of aloofness indeed.

 

For working Marble the easiest way is using carbide tipped tools, due to its hardness of 3 to 4 Mohs. One must consider though that the impact of the punch or chisel does not only affect the immediate surface but sends a shockwave into the crystal structures which causes milky, flat coloured spots. Marble needs to be caressed or it will turn a Diva...


Serpentine

is the common denomination of rock which was baked from various elements deeply in the earth crust and which was later pushed to the surface by tectonic movement, usually in the form of nodules. As differently as the elements embedded in the various serpentine (i.e. magnesium, iron, nickel, cobalt and many more) are, as differently are the locations where Serpentine is mined. This includes Asia (India, Turkey, Taiwan) as well as Europe (Italy, France, Germany, Poland, Croatia and many more), Cuba and Africa (Ethiopia, South Africa, Zimbabwe).

 

The coloration of Serpentinites ranges from cream white (White Opal) through honey- and caramel coloured (Fruit), reddish-white-greenish banded (Cobalt Serpentine), various hues of green (Green Opal, Leopardstone) to brownish-black (Black Serpentine) and rich, deep black (Springstone). The hardnesses vary as well, from about 2.5 (Green Opal) to slightly above 4 Mohs (Springstone).

 

The exceptionally vivid colours and the relatively uncomplicated behaviour of many Serpentines (mainly Fruit, Cobalt and Springstone) is one of the reasons I like to work this stone very much. Serpentinites are really co-operating well with normal forged hand tools and you can polish them in many degrees, from semi-flat to high gloss. Especially the change between polished and raw, broken areas make Serpentine sculptures very appealing because here the rich, intense colours of the polished faces contrast very lively with the hard, structured and paler areas of the stone.

 

I prefer Serpentine from Zimbabwe because this is the stone which made me enter the "real" stone sculpting. The deposits in Zimbabwe are mainly in the "Great Dyke" area, a ridge that crosses the country roughly north-to-south. During that course the Great Dyke passes the Guruve District, approx. 170km (about 105 miles in old money) where the artist village of Tengenenge (in Shona language "the beginning of the beginning") is situated, showing probably the world's highest stone sculptor density per square meter. From here originate the artists Richard Kambuzuma, Sydney Majengwa, Washington Matafi, Godfrey Matungamidze and most important (to me) of all Merchers Chiwawa, who showed me the way of stone sculpting and who ignited in me the love and desire to find the soul in the stones.

 

Because  my suppliers stock the raw Serpentine stone in the shape of broken (not cut) pieces of very different size, there are always some pieces that whisper to me "take me, I contain something really special!" and until today, none of these candidates has cheated me. The only thing I wish for (sometimes) is a car with a bigger load capacity...