# Notes on the Nature of "Creta Anularia" and Vitruvius' Recipe for Egyptian Blue

Fréderic Davidovits

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Fréderic Davidovits. Notes on the Nature of "Creta Anularia" and Vitruvius' Recipe for Egyptian Blue. Colours in Antiquity, Edinburgh University, Sep 2001, Edinburgh, United Kingdom. pp.16-21. hal-04049203

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# Notes on the Nature of *Creta Anularia* and
Vitruvius' Recipe for Egyptian Blue

Frédéric Davidovitsª

*Published: Frederic Davidovits, "Notes on the Nature of 'Creta Anularia' and Vitruvius' Recipe for Egyptian Blue", L. Cleland, K. Stears, and G. Davies (eds), Colour in the ancient Mediterranean World, Oxford: BAR International Series 1267, 2004, p. 16-21.*

## Abstract

*Notes on the Nature of Creta Anularia:* In Latin, the word creta indicates generally a dry and soft substance that is not plastic. In Roman painting, creta anularia (Vitr. 7, 14, 2; Plin. nat. 35, 46) is mixed with pastel dye (Isatis tinctoria); it absorbs the blue-purple colouring agent to make it insoluble in water. Another description of creta anularia is in Pliny nat. 35, 48: "Anulare quod vocant, candidum est, quo muliebres picturae inluminantur; fit et ipsum e creta admixtis vitreis gemmis e volgi anulis, inde et anulare dictum".

By referring to this text by Pliny the Elder, modern archaeometrists designate under creta anularia a white pigment consisting of chalk and crushed glass. However, it is generally admitted that this text by Pliny does not describe a pigment, but rather a make-up. Plautus, (Most. 1, 3 v. 258, Truc. 1, 4, v. 290) cites products usually used in paintings, as being also used for make-up. If wall colours can be used as make-up, it is hard to understand how a mix made of chalk and crushed glass, or a siliceous chalk (the creta anularia of the archaeometrists) could be appropriate. These abrasive substances would hurt the skin. There exists a category of minerals which fit exactly with the properties claimed for the creta anularia in Pliny's text. They as soft, easy to crush and have the property of reflecting light (inluminantur): it is mica, a natural soft creta well adapted for skin make-up. The geological micas powder layers contain also coarser flakes or bigger crystals, which are well suited for the manufacture of cheap false precious stones (vitrea gemma) mounted on popular rings, hence the name of creta anularia.

Vitruvius' Recipe for Egyptian Blue : C. Vestorius, a rich banker of Puozzoli, businessman, correspondent of Cicero and Atticus, imported and perfected in Italy the Alexandrine methods of manufacture of the pigment Egyptian blue. The text of the Roman architect Vitruvius (7, 11, 1) is the only text which outlines the manufacture stages of this artificial pigment based on copper oxide and alkali. The Egyptian blue is a calcium-sodium disilicate of copper (CaO, Na₂O) CuO 4 SiO₂. Vitruvius' blue *caerulea* is shaped into blue or green balls. One crushes sand (*harena*) with natron (*flos nitri*); one obtains a sort of flour and mixes it with copper; this mixture is shaped into a ball, dried in air and fired in earthenware pots.

Yet, the scientific analyses of *caerulea* show the presence of a high amount of calcium. But Vitruvius's text does not mention any addition of limestone or lime. How was the calcium brought in the mix ? The source for the calcium might be the natural *harena*

<footnote>ªConferences held in September 2001.</footnote>
(sand) like the *harena fluviatica* extracted from the river Volturnus in Campania, also
used for the manufacture of glass (Plin. *nat.* 36, 194). It is a silico-calcareous sand.
Faventinus (5, p. 308) describes a powder of “harena” (*pulvis harenae*). An other CaO
source is the *flos nitri*, which is usually washing soda or natron, and acts as a flux. Pure
washing soda does not contain lime. However, Pliny (*nat.* 31, 114), states that in Egypt
natron is falsified with some lime, a forgery detected by it taste. It can be assumed
that the *flos nitri* described by Vitruvius was imported from Alexandria and contained
a fraudulent amount of lime.

To sum up: there are two possible sources for calcium in Vitruvius’s text: one is a
calcareous *harena* or a mixture of silico-calcareous sand; the second is a falsified natron,
like the one commonly sold in Egypt.

The Nature of *Creta Anularia*

**Introduction**

In Latin, *creta* generally indicates a dry, soft substance, which is not plastic. *Creta* is a generic term referring to a variety of substances used in agriculture, ceramics and painting. Referring to Pliny, F. Bearat defines *creta anularia* as a white pigment, used in painting, consisting of chalk mixed with crushed glass (N. H. 35.48 ; 1997 : 22). These notes will first study the characteristics of *creta* as described in Roman technical literature, then determine the specific nature of *creta anularia*, described as a variety of white pigment by Vitruvius (7.14.2) and Pliny (N. H. 35.46).

*Creta* (often translated ‘chalk’ or ‘clay’) has a wide polysemy (Lambertz 1906 : 1184-7). From a technical point of view, it is generally defined as: a kind of rock extracted from the ground: a dry powder which is soft to the touch and does not irritate the skin. Another distinguishing feature is mentioned by Lucretius (3.381) :

nam neque pulveris interdum sentimus adhaesum / corpore nec membris
incussam sidere cretam.

"For sometimes we do not feel dust clinging to the body, or chalk-powder
settling upon the limbs." (Rouse 1963 : 197)

Here *creta* is used to whiten clothes (Ernout 1959 : 100) and is so finely ground that no-one can feel it. Since it is a soft powder, *creta* cannot be siliceous sand. or hard limestone. or granite etc.

The polysemy of *creta* in the technical literature

In technical contexts, all types of *creta* (clay, chalk, talcum, etc.) are processed to eliminate hard elements, yielding a material suitable for various applications. Vitruvius provides an overview, in his *De Architectura*, of the variety of *creta* materials.

1) An underground clay, supplying muddy water (8.1.2) <fnref n="1" />

<footnote n="1">¹ In agriculture, *creta* means ‘chalk’ (Varro *Rust.* 1.9.2) or ‘clay’ (Palladius 1.5.1) or both (Vergil Georg. 2.214-215).</footnote>
2) Ceramists'/ builder's clay "For brickwork that is not made of good clay [bona creta] or is too little baked [cocta] shows its faults on the work when weathered by ice or hoar-frost"(2.8.19). For Vitruvius, creta is a material ready to be used by the homo faber. Here 'clay' creta has been refined becoming 'good' for manufacturing bricks. In other parts of De Architectura, creta is synonymous with argilla, the plastic clay used by ceramists. <fnref n="2" />

3) Coloured pigment or pigment filler :

7.3.3 : "chalk-powder" (white) for tempera <fnref n="3" />

7.7.4 : "green clay" for painting.

7.14.1-2 : support for pigments in paints: creta, creta selinusia, creta anularia.

Other latin authors mention uses of creta :

- for cosmetics <fnref n="4" />

- for cleaning or whitening clothes <fnref n="5" />

- for cleaning silver <fnref n="6" />

- for enriching agricultural soils <fnref n="7" />

In these examples, *creta* is a material which is extracted then crushed. All these uses are linked by denoting a fine material, soft to the touch. If most of the *cretae* are thus explained, still the nature of the *creta anularia* remains to be determined. <fnref n="8" />

*Creta anularia*

*Creta* appears as a fine-filler in paints, absorbing the soluble organic dyestuff to render it insoluble, like a mineral pigment.

Item propter inopiam coloris indici *cretam* selinusiam aut *anulariam* uitro,
quod Graeci ἵσατιν appellant, inficientes imitationem faciunt indici coloris.
(Vit. 7.14.2)

"Also, because of the scarcity of indigo they make a dye of chalk from Selinus,

<footnote n="2">² 2.8.19 ; 5.12.5 ; 8.1.5 ; also called *creta figlina* : Varro *Rust.* 3.9.3 ; Pliny the Elder *H. N.* 10.50 ; 15.64 ; *creta figularis* : Columella 6.17.6 ; Celsus 1.3 ; and Pliny the Elder *H. N.* 31.47 ; *creta figulinarum* : Pliny *H. N.* 14.123 ; 15.60 ; *argilla* : Cato *Agr.* 40.</footnote>

<footnote n="3">³ Cf. Plin. *H. N.* 33.162 ; 35.49 ; Varro *Rust.* 1.57.2.</footnote>

<footnote n="4">⁴ Plautus *Truc.* 294; Aul. 718; Novius *Atell.* 84; Horace *Epod.* 12.10; Ovid *Ars* 3, 199; Petr. 23; Mart. 6.93.9; 8.33.7 etc.</footnote>

<footnote n="5">⁵ Plautus *Aul.* 718 ; *Poen.* 969; Titinius 29, Pliny *H. N.* 17.45 ; *creta fullonia* ; 35.196-8. Fuller’s earth can be : bentonite, montmorillonite, kaolinite, cimolite (bentonite + alunite), gypsum, talcum, steatite, etc. Bailey 1932 : 244-5 ; Robertson 1949 : 51-2 ; Augusti 1962 a : 131-2 ; 1967 : 47 ; Croisille 1985 : 289-90.</footnote>

<footnote n="6">⁶ *Creta argentaria* : Pliny *H. N.* 17.45 ; 33.131 ; 35.199 ; Cicero *Ad Att.* II.3. This would be a siliceous earth, chalk, talcum, steatite, or cimolite : Bailey 1932 : 218, 244 ; Augusti 1962 a : 132 ; 1962 b : 138-9 ; 1967 : 58-9 ; Croisille 1985 : 290-1.</footnote>

<footnote n="7">⁷ *Marga, fossicia creta:* Pliny *H. N.* 17.45-6 ; 17.48 ; Columella 2.15.4 ; 5.8.6 ; Varro *Rust.* 1.7.8.
This would be phosphatic earth, marn, talcum, steatite, André 1964 : 127-9.</footnote>

<footnote n="8">⁸ Vit. 7.14.2 ; Pliny *H. N.* 35.46 ; 35.48 ; Isidorus of Sevilla *Orig.* 19, 17, 22.</footnote>
or from broken beads. along with woad (which the Greeks call *isatis*) and
obtain a substitute for indigo."

(Granger 1985 : 129; Liou *et al.* 1995 : 37)

This description belongs to a section in which Vitruvius describes organic pigments extracted from plants as cheaper replacements for the expensive pigments: *sil*, purple, indigo and *chrysocolla*. <fnref n="9" />

Unfortunately, Vitruvius does not give any more information about *creta anularia*. but Pliny mentions it several times. The first (N. H. 35.46) adds nothing. In contrast, at 35.48, he provides interesting information, describing two inexpensive colours of his time : a green called *appianum* which was used in imitation of *chrysocolla*, and *creta anularia*, which had a white colour.

Anulare quod vocant, candidum est, quo muliebris *picturae* inluminantur ; fit et ipsum e creta admixtis vitreis gemmis e volgi anulis, inde et anulare dictum.

Rackham (1968 : 297) provides two possible meanings :

"The other colour is that called 'ring-white,

1) which is used to give brilliance of complexion in painting of women,

2) which shines on the painted face of women,
this itself is also made from white earth mixed with glass stones [*vitreis gemmis*] from the rings of the lower classes, which accounts for the name *ring-white*."

Rackham hesitates to translate *pictura*, because it may denote either 'paint' or 'make-
up'. In order to establish which is more appropriate, the technical context will be ex-
plored.

The nature of *creta anularia* in archaeology

Several hypotheses have been made concerning this creta. For Augusti (1962 a : 131; 1962 b : 138-9; 1967 : 57-8) it is a siliceous product used in the manufacturing of lacquers, although no trace was found at Pompeii. For Bearat, it is a mixture of chalk and crushed glass used in Roman wall paintings at Avenches, Switzerland, and in Pompeii (1997 : 22). For Bailey, commenting on 35.49, it is a make-up :

"When other better pigments were available, it seems rather unlikely that anulare would be sufficiently prominent in the artist's palette to be mentioned by Pliny in this way. On the other hand, a cheap pigment might well be in favour with the lower-class women who constantly cross the pages of Plautus and others with painted faces." (Bailey 1932: 221)

Indeed, in two of Plautus’ plays there are mentions of pigments, employed not only
in painting, but also as make-up.

<footnote n="9">⁹ For woad in Roman wall painting, Augusti 1967 : 119-20.</footnote>
“Scapha: When you’re pretty yourself, you can be positive your hair is pretty.

Philolaches : (aside) Bah ! Can you mention anything worse than that woman, there ? Now she’s all compliments, the slut ! A moment ago, she was all contradictions ?

Philematium : Give me the ceruse [Cedo cerussam].

Scapha : Ceruse, indeed ! What for ?

Philem. : To rub on my cheeks.

Scapha : You might as well expect to white ivory with ink.

Philolaches : (aside) Very neat — ivory and ink ! Bravo, Scapha ! Congrat-
ulations !

Philem. : Well, then, give me the rouge [cedo purpurissum].

Scapha : No, I won't. Lots of sense you show. You want to daub fresh paint on a perfectly lovely picture [Nova pictura interpolare vis opus lepidissimum] ? Girls of your age shouldn't touch a bit of colour, or ceruse [cerussam], Melian cream [melinum], or any other cosmetic.

Most. I, 3, v. 250-64 (Nixon 1950 : 128-9)

“Astaphium : (meltingly) Oh dear me ! Why, I merely blushed because
you yelled so.

Truculentus : Hey ? Blushed, did you ? As if you’d really left room for colour on any part of you, you wicked girl. You’ve daubed your cheeks with red-chalk [rubrica] and the rest of your body with clay [creta]. You’re just awful creatures.”

Truc. II, 2, v. 291-4 (Nixon 1952 : 254-5)

In these two texts, Plautus describes coloured pigments (usually used in painting : *purpurissum*, *melinum*, *rubrica*, *cerussa*, *creta*) being used as cosmetics. and on this basis, commentators on Pliny consider *creta anularia* more as a make-up than a paint, because it was cheap. <fnref n="10" />

Plautus’ use of *pictura* (one of the term ’s first occurences) is recognised as metaphor-
ical, but commentators have not considered Pliny’s use of *pictura* as such (Bailey 1932
: 221; Croisille 1985 : 165). If *creta anularia* was a makeup, its physical nature is not
well determined. Indeed, Bailey indicates uncertainties : how the pigment was prepared
*admixtis vitreis gemmis* ; if intact stone imitations were added, since it seems improbable
they were crushed ; and whether it was *creta* with added glass (Bailey 1932: 221).

A *creta* containing glass, or siliceous chalk (mixed carbonate of calcium and silica: Augusti 1967: 57-8) would contain hard elements, risking harm to the skin. Such materials are absolutely inappropriate for make-up. Furthermore, powdered glass does not *inluminantur* reflect light, since it has no facets. Crushed quartz or rock crystal, which do, also have an abrasive quality.

There is, however, a type of rock which is easy to crush into a soft powder and reflects light: the micas. This group includes minerals (such as muscovite, biotite, pligopite, and lepidotite) which are low on Mohs' scale (2-3) and can be of various colours: white, light yellow, amber, green, brown, black, lilac, grey, or pink (Pough 1960: 258-62; Mottana

<footnote n="10">10 Bailey 1932 : 221 ; Croisille 1985 : 165.</footnote>
et al. 1993: 232-40). They have a 'glassy brightness' and most resemble iridescent shell.
Mica fulfils the criteria for *creta anularia*.

It becomes clear, then, that in Pliny's text, the phrase *vitrea gemma* designates the micaceous plates. They could be large beads or crystals, used as stone imitations for rings or cheap showy jewellery. Therefore, we can agree with Rackham's second suggestion, and so propose the following translation.

"The other colour is that called ring-white, which shines on the make-up
[picturae] of women. This itself also is made from white earth mixed with
micaceous precious stones from the rings of lower classes, which accounts for
the name ring-white."

Pliny *N. H.* 35.48

## Conclusion

*Creta anularia* can be defined as a mixture of chalk and white mica, which was used for both painting and make-up. The geological micas, when not crushed and ground, contain coarse flakes or big crystals, which would be well suited to the manufacture of cheap, false, precious stones (*vitrea gemma*) mounted on popular rings — hence the name of creta anularia. Materials involving crushed glass mixed with chalk, like those found in Roman archaeology, do not correspond to a *creta*, and therefore may not be called *creta anularia*.
Vitruvius' recipe for the manufacture of the pigment 'Egyptian blue'

**Introduction**

C. Vestorius, a rich banker, businessman, and correspondent of Cicero, perfected the Alexandrine method of manufacturing the pigment 'Egyptian blue' at Puozzoli. <fnref n="11" /> He even invented an eponymous new nuance of excellent quality blue, the *lomentum Vestorianum* (Pliny *N. H.* 33.162). Vitruvius may have visited his factory :

"The processes for making blue were first discovered at Alexandria; afterwards also Vestorius founded a factory at Puteoli. His method and his ingredients are sufficiently noteworthy. Sand [harena] is ground with flowers of soda [nitri flore] to such fineness that it becomes like flour. Cyprian copper [aes cyprum] is sprinkled from rough files like fine dust so that it combines with the mixture. Then, it is rolled by hand into balls and they are put together to dry. When dry they are collected in an earthenware jar, and the jars are put in a furnace. In this way, the copper and the sand burning together owing to the vehemence of the fire dry together, and, interchanging their vapours, lose their properties ; and their own character being overcome... they acquire a blue colour." Vitruvius 7.11.1 (Granger 1985 : 122-5; Liou *et al.* 1995 : 34-5)

No other extant text describes the steps of manufacturing this artificial pigment (based on copper oxide and an alkali) which was made, at a consistent level of quality, from the early Egyptian periods to the Roman, when it was used for frescoes and other paintings. <fnref n="12" /> This paper compares Vitruvius’ text with our other linguistic and technical evidence.

**Definition of ‘Egyptian blue’**

'Egyptian blue' is an artificial product : a calcium-sodium disilicate of copper. It was an expensive pigment unaltered by lime in wall painting, <fnref n="13" /> and commonly shaped into blue or green balls called *caerulea*. <fnref n="14" /> There are several types of 'Egyptian blue':

- *caeruleum aegyptium*

- *caeruleum vestorianum*

- *caeruleum puteolanum*

- *coelon*

- *lomentum* (Augusti 1967 : 47, 62-70, 72, 147)

<footnote n="11">¹¹ Gundel 1958 : 1789-1790 ; Tchernia 1968-79 : 51-82 ; Camodeca 1977 : 62-98 ; Sirago 1979 : 3-16 ; D'Arms 1980 : 78-80 ; 1981 : 49-55 ; Andreau 1983 : 9-20 ; Morel 1983 : 291-320 ; Lavagne 1988 : 430-6.</footnote>

<footnote n="12">¹² Theophrastus *Lap.* 55 and see Eremin, this volume (in "Colour in the ancient Mediterranean World"); Caley 1945 : 152-6 ; Gettens & Stout 1946 : 112-3 ; Ullrich 1987 : 323-332.</footnote>

<footnote n="13">¹³ Pliny, *N. H.* 33.161-2 ; 35.45, 49 ; Cetius Faventinus 27. 10.</footnote>

<footnote n="14">¹⁴ Blümner 1887 : 499-508 ; André 1949 : 162-171 ; Forbes 1955 : 214-9 ; Augusti 1967 : 45 ; Reinach & Rouveret 1985 : 13.</footnote>
The modern theoretical process for its fabrication is as follows : siliceous sand is mixed with sodium carbonate, calcium carbonate, and copper, obtaining crystals of the disilicate, surrounded by green sodic silicate glass (Ullrich 1987 : 323-6). Lime (calcium carbonate) lowers the melting point of the mixture : the blue crystalises better. ‘Egyptian blue’ can be defined as a ceramic, and as a glass (Delamare 1997: 104-6). Archaeometrists distinguish two products with the same appearance but differing chemically : ‘Egyptian blue’ and ‘Hubert’s blue’ (Onoratini et al. 1987 : 651-3).

### Egyptian blue

One unit of calcium oxide (CaO) is mixed with one unit of copper oxide (CuO) four units of silicon oxide (SiO₂) and 0.6 unit of sodium carbonate (natron : Na₂CO₃ · H₂O). The mixture is calcined at 850 °C for twenty-four hours. The result is calcium-sodium disilicate of copper (CaO, Na₂O) CuO 4 SiO₂.

### Hubert's Blue

One unit of copper oxide (CuO) is mixed with one unit of sodium oxide (Na₂O) and four units of silicon oxide (SiO₂). The mixture is calcined at 800 °C for two hours. The result is a triclinic crystal of anhydrous sodium copper silicate Na₂CuSi₄O₁₀.

Analyses of eight *caerulea*, found in Fréjus (France) and in two Roman shipwrecks, describe them as a ceramic, porous product, in which there are crystals of ‘Egyptian blue’, quartz, impurities, and glass (calcium-sodium copper silicate) (Onoratini *et al.* 1987 : 652-3).

### Lack of calcium in Vitruvius’ recipe

Vitruvius’ ingredients are sand (*harena*), flowers of soda (*flos nitri*) and Cyprian copper (*aes cyprum*). In the Middle-Ages, artisans who followed this Vitruvian recipe obtained ‘green frit’ and not ‘Egyptian blue’ (Ullrich 1987 : 327) because it apparently contains no calcium (calcium carbonate/lime). However, there are two possible hidden sources of calcium in the recipe.

### *Harena* - ‘sand’

Cetius Faventinus summarizes Vitruvius’ recipe :

Caerulei temperationes Alexandriae primo sunt inuentae; nunc autem Puteolis ex harenae pulvere et nitri flore temperature; aes cyprium adustum <...> (27. 10)

“The processes for making blue were first discovered at Alexandria; now it is made at Puteoli and it is a combination of crushed sand and flower of soda; but (if) copper is calcined...” (Cam 2002 : 36, 146-7 the rest of the Latin text is uncertain and a correction would be: *si et Cyprium adustum < fuerit cum hac mixtione, caeruleo redigetur colore >* ‘but if copper is calcined with this mixture, it becomes blue’.)

‘Sand of Alexandria’ used in glass- and blue-making processes has 35 % calcium oxide (CaO, Pigianol 1965 : 81). Vestorius’ factory was near the Volturnus river, sand from
which was used in glass manufacture (Ullrich 1987 : 327 ; Crimaco 1991 : 11-16) so it
can be assumed that Vitruvius' *harena* meant a silico-calcareous sand extracted from
this river. *Harena* is therefore a possible source of calcium.

Flos nitri - ‘soda’

In ‘Egyptian blue’ and glass-making processes, soda is used as a flux agent. But pure
soda (Na₂O₃ Greek *nitron* or *litron*. Latin *nitrum*) <fnref n="15" /> does not contain calcium. On the
other hand, Pliny writes :

Nitri probatio ut sit tenuissimum et quam maxime spongeosum fistulosumque.
Adulteratur in Aegypto calce, deprehenditur gustu. Sincerum enim statim
resoluitur, adulteratum pungit cake et aspersu reddit oderem vehementer.
(N. H. 31.114)

"The tests of soda are that it should be very fine and as spongy and full of holes as possible. In Egypt, it is adulterated with lime, which can be detected by the taste ; for pure soda melts at once, but adulterated soda stings because of the lime, and gives out a strong, bitter odour." (Jones 1963 : 448-9)

Therefore it can be assumed that the *flos nitri* described by Vitruvius was imported
from Alexandria, and contained a certain amount of lime.

Conclusions

Firstly, Vestorius would have built his factory in Puzzoli for several reasons : <fnref n="16" />

- Puteoli was the biggest port in Italy (before the organisation of Ostia under Claudius' administration) and an important commercial and industrial area (Dubois 1907 : 70-1: Morel 1979: 21-39: Fraser 1986 : 156-7).

- Local *harena* from the Volturnus river naturally contains a sufficient quantity of calcium oxide, as in Alexandria.

- ‘Egyptian blue’ and glass manufacture require the same raw materials.

Secondly, there are two possible sources of calcium in Vitruvius’ text :

- silico-calcareous sand.

- adulterated natron commonly sold in Egypt.

Taking these two sources of calcium into consideration as part of Vitruvius’ recipe provides the correct ingredients and procedure for the manufacture of ‘Egyptian blue’. In this paper I have pointed out that archaeometrical studies alone are not sufficient to understand ancient technology. It is only when archaeometry is associated with linguistic and technical study of ancient texts that it is possible to discover the original ingredients and processes used in the related antique technology. Both investigation methods (the scientific and the linguistic) are complementary to each other and should be practised accordingly in any study of ancient technology.

<footnote n="15">¹⁵ Dioscorides 5.113 : Pliny N.H. 31.106-122 ; 33.93 ; Forbes 1955 : 174-9 : 1957 : 110-8.</footnote>

<footnote n="16">¹⁶ Dubois 1907 : 128. 238. Cf. *CIL* X. 1631.</footnote>
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