Sunday, June 30, 2013

Architectural Word of the Day; 1 - 10


A capital is the uppermost termination or 'head' of a column. Unsurprisingly, our English word “capital”

directly derives from the Latin ‘caput’ simply meaning ‘head’.

Many of our apparently abstract architectural terms in English are anglicized French, Latin and Greek words. As with our initial example of ‘capital’ we’re going to explore how so many of these terms are nothing more than everyday words used as a metaphor for what an architectural element visually resembles or what function it holds.


Sounds so exotic, right? Well it’s just what it looks like. In ancient Greece they called it ‘bous’ (βοῦς) meaning ‘ox’, ‘kranion’ (κρανίον) meaning ‘skull’. Yep, just plain old ox-skulls.

The reason this became an important motif for the Greeks in temple architecture stems from religious ceremonies that included sacrifices of oxen to the gods. Early on they used to actually mount the sacrificial skulls but eventually the stylization of the ‘bucranium’ was carved in relief directly into the frieze of the temple.


When it came to architecture the Greeks and Romans had style…and it usually came in groups of 4, 6, 8 or


What do I mean by that? The ancient Greek word ‘stylos’ (στῦλος) meant column or pillar. For example a temple front that had 6 columns in front would have been called ‘hexastyle’ or six column temple. The image attached is an example we all recognize of a ‘tetrastyle’ or four column portico.


This term used to described a deeply sunken ceiling panel has its origin in an everyday item it resembles. The ancient Greek word ‘kophinos’ (κόφινος) refers to a common basket.

Notice the stylized flowers filling the ‘baskets’ of this coffered dome.


Characterized by the large, sprial volutes this style became fully developed in Greek Ionia, modern day
beautiful rendering by Steve Shriver
Turkey. In Greek mythology, Ion was the progeny of Apollo and often temples prominently featuring Ionic designs were dedicated to him.

However, the origins of the Ionic go back further east to Mesopotamia, Persia and the Indus Valley. For example, the Torah indicates that Noah’s grandson, ‘Javan’ (the Hebrew variant of Ion), was the forefather of the Greek people.


The pediment is typically the dominant feature of a façade surmounting a row of columns or crowning a door or window.

Although there are many variations the oldest and most common shape forms a triangular gable. The name 'pediment' is thought to be a mispronunciation of 'periment', itself an alteration of the Egyptian 'pyramid' whose shape it resembles. 


Of singularly English origin, fan vaulting in stone is a development of the third and last period of Gothic architecture, the Perpendicular. The earliest extant example may be found in Gloucester Cathedral, circa 1351.

It would later be emulated in Gothic Revival architecture as a purely decorative ‘fan tracery’ of ceilings in plaster. The 1852 renovation of the ceiling of the Unitarian Church in Charleston, South Carolina is a great American example.


For the Greeks ‘doma’ (δωμα) simply meant a domestic ‘house’. However, with the spread of Christianity

basilicas with a resident bishop came to known as the Lord’s house, abbreviated to ‘duomo’ in the vernacular Italian.

Sometime in the 17th century, the English modified ‘duomo’ to describe the ‘cupola’ crowning many of these prominent Italian basilicas.


This is the stone that lies at the apex of a masonry arch. It must be angled, wedge shaped to receive the opposing stresses for the arch not to collapse.

As this is a natural focal point such as for the arched entrance to a building the keystone is often beautifully decorated with a motif that carries meaning for the owner or institution.


The term ‘architrave’ has a divided heritage. The prefix, ‘archi-’ indicates that what follows is of great importance. A Greek leader was titled an ‘archon’ (ἄρχων) to denote his primary status.

‘Trabem’ on the other hand was the Latin word for ‘beam or timber’. Thus an ‘architrave’ is the great beam resting atop the columns and the primary support for the roof above. 

Contributed by Patrick Webb  

Plaster Word of the Day; 1 - 10

Image courtesy of Plâtres Vieujot

One of the foundations of a good trade education is understanding the vocabulary of that trade. So for a plaster education we’ll begin with the most fundamental of terms, Plaster.

In some languages and localized areas of the English speaking world plaster is ‘mineral specific’, such as a gypsum derived material, or ‘use specific’ such as a coating applied in interior. However, our English word “plaster” ultimately derives from the Greek ‘emplastron’ (εμπλαστρον) meaning “to daub on”.

So the term “plaster” can rightly describe a variety of interior or exterior coatings that are daubed, thrown or trowel applied.


Finally we have an English word that has its roots in…English!
Screed is an Old English word that originally meant a strip of cloth but eventually came to mean a strip of anything. In fact, ‘shred’ has the very same etymology.

In plastering it refers to strips serving as a termination and guide for the larger infill areas. Often if wood, metal or non-plaster materials are used it will be referred to as a ‘ground’. However, if the strip is made of plaster it maintains the name screed.

Also, a screed is a generic term for the straight edge used to level the infill surface and the act of leveling is called ‘screeding’. There are a variety of screeds that have specialty applications with names such as rods, darbies, slickers etc.


This grouping of vocabulary comes from across the pond, common terminology in the UK and Ireland.

It is most descriptive (but not exclusively) of the traditional 3 coat lime plastering system used over monolithic substrates such as brick or stone.

The RENDER is the first coat of plaster, the ‘coarse stuff’ with large, sharp aggregates. It is applies rough and and gets scratched up to provide a mechanical key or bonding surface for the next coat.

The FLOAT is the next coat with the same material. However, the surface is scoured, compressed and leveled with a wooden hand float, hence the name.

The SET, is the final coat. This is the final mix with lime putty and fine aggregates with Plaster of Paris (gypsum plaster) added to initiate a 'set' or firming up of the lime.


Image courtesy of Plâtres Vieujot
The Greek work ‘gypsos’ (γύψος) described the mineral that we today identify as gypsum.
Gypsum plasters may contain sand and small percentages of other binders such clay or lime.
Many useful gypsum plasters are in fact a blend of different types of gypsum:

Gyp – Pulverized gypsum with the chemical designation hydrated calcium sulphate (CaSO4•2H2O). Often used as a natural accelerator in gypsum plaster.

Beta Gypsum – Gypsum baked at a low temperature to form calcium sulphate hemi-hydrate (CaSO4•~0.5H2O). Also, known as Plaster of Paris.

Alpha Gypsum – The hemi-hydrate form baked under higher barometric pressure. The resulting material can have up to 10 times the compressive strength of beta gypsum.

Anhydrous Gypsum – Gypsum baked at a higher temperature to form pure calcium sulphate (CaSO4). Often used as a natural retarder in gypsum plaster.


Also known as a ‘felt brush’ or just a ‘mop’.

This is an effective tool for moisture management when finishing clay, lime or gypsum plasters.

The release of water is directly related to pressure applied. Over-saturated areas common with sponges and pump sprayers are easily avoided with a blister brush.


Image courtesy of Plâtres Vieujot
This technique of carving into a plaster to reveal a contrasting colour underneath is very much associated with the Italian tradition from whom we have directly borrowed the word sgrafitto meaning ‘scratched’. However, the Italians in turn had borrowed the term from the Greek ‘gráphein’ (γράφειν) meaning to write.

From the same origins the Germans first coined the common designation for the form of carbon useful for writing, ‘graphite’.


Plaster mouldings can either be formed 'in place' or on a flat table or 'bench' to be later applied.

When formed on a bench typically Plaster of Paris, moulding plaster is used which has a rapid set. You have to move quickly when using pure moulding plaster hence the term 'running'.


The technique of chiseling into fresh plaster in deep relief in situ (called ‘gebs’ in Arabic) is a craft that was developed to perfection by the Moors. After the expulsion of the Moors from the Iberian peninsula Muslim artisans were given opportunity to convert and some continued their craft in Christian motifs developing a very rich tradition in Provence.

Gypsum is the ideal medium for this technique. While fresh gypsum plaster is soft enough to easily carve it has great plasticity and will not easily crumble. This makes it possible to achieve deep undercuts with sharp edges and thin details that soon develops hardness and durability as the plaster dries and fully cures.

Contributed by Patrick Webb 

Thursday, June 20, 2013

Moulding Theory

Image courtesy of Vicat
The art of plastering is itself divided into two major fields of employ. Rendering is fundamental. A plaster apprentice first learns to ‘tend’, to prepare various binders such as gypsum, lime or cement into a workable plaster mix. As he progresses, he then learns how to ‘square’ a room, establishing centerlines, benchmarks and grounds. His education culminates in mastering the art of rendering plaster, applying plaster in successive coats until he achieves a smooth and planar surface.

Many plasterers make a good living with rendering skills alone. However, for the ambitious, once mastery of rendering has been achieved a plasterer may progress unto run moulding work. As is the case with all moulding mediums, plaster moulding is an art strongly allied to the field of architecture. A number of treatises, books and papers have been published from the Renaissance through the 20th century on the theory of moulding design.

I will attempt to briefly present three ways of considering moulding design using metaphors of language: Vocabulary, Grammar, and Composition. As is the case with language, we can think of each section as a progression building towards higher levels of sophistication.


In language vocabulary is the set of words that are familiar to a person or group of persons.
It is a fundamental of speech and communication. To create intelligible mouldings architects and artisans also have need for a common vocabulary.

The vocabulary of mouldings can be defined as the most basic elements found within a moulding. The shape of a given moulding is determined by its profile. In the case of plaster this profile is in the form of a knife that ‘cuts’ the hardening plaster. A given profile will contain several ‘elements’ or individual shapes that make up the profile. These individual shapes each have a specific geometry that can be identified. Our moulding vocabulary can likewise be thought of as the pure geometric forms found within a moulding.

We can group individual elements in a profile by their geometry. Below are a few examples sorted under the four major geometries:

Image courtesy of Palladio Mouldings
Straight: fillet, fascia, chamfer

Concave: cavetto, scotia, congé

Convex: ovolo, torus, astragal

Compound: cyma recta, cyma reversa, beak


Every language needs rules, structure, otherwise known as grammar. Just as individual words or vocabulary perform a function (noun, verb adjective, etc.) within a sentence, individual moulding elements manifest an architectural function within a profile. Let’s consider each of the five of the principal architectural functions of mouldings individually.

Terminating: cavetto, cyma recta

Terminating elements are often found at the top of a cornice or other crowning feature. Because most of its form is void, it conveys lightness but an inability to support a load so therefore is not generally appropriate lower in a profile.

Supporting: ovolo, echinus

In direct contrast to the aforementioned terminating elements are supporting elements. The robust, sturdy shapes of these elements imply a capacity to support significant weight above it. Supporting elements are prominently featured as bed mouldings where they appear to support a projecting crown.

Binding: torus, thumb, astragal

As the name implies binding elements encircle an object as if it were holding it together. Various half round elements such as tori or astragals are commonly found at necks and bases of columns.

Separating: bead, fillet, scotia

Separating elements typically are smaller in scale to binding elements. As such, beads and fillets create division and clarify transitions from one larger element to the next.

Prone: cavetto, cyma reversa

Transitions from vertical wall surfaces to horizontal floor surfaces indicate a transfer of weight. Prone mouldings can simultaneously provide a graceful translation from one vertical plane to the next such as the bottom of a wall or column to the top of a base or plinth.

running a moulding on a bench


Upon mastery of vocabulary and grammar we have all the tools necessary to compose a moulding profile or even an entire elevation. Of course, we’re faced with the traditional challenges of any author of creating an intriguing story! Next are a few principles to keep in minding in moulding composition.

Harmony is very important both within a moulding and throughout an entire elevation. One of the most harmonizing factors is to maintain a common facial angle common to all mouldings. In Roman and Renaissance architecture 45° was a common angle whereas 60° was used more often by the ancient Greeks. Too much harmony, such as repeating the same elements at the same scale, can lead to monotony.

Rhythm can provide welcome contrast. Alternating straight and curved elements is one way of providing rhythm. Contrasting concave and convex curves is also very effective. Radial curves provide a very even gradation of shadow whereas curves of conic sections (parabolae, hyperbolae and ellipses) provide sharper transitions and more contrast. For many theorists the study of the shadow created is more important than the profile itself.

Dominance is a principle that can define the feel of a moulding, elevation or an entire building. The addition of 'ears' or an over door to an entry can indicate its hierarchy over lesser doorways. Dominance can also be achieved by use of scale, exaggerating a supporting or terminating element throughout the composition i.e., to establish an overall feeling of delicacy or ruggedness.

A Classical Example

The Attic Base is the most used column base in Classical and Gothic architecture and is found in other vernacular architectural styles around the world. Let’s break it down to its constituent elements and see how much of what we have previously considered applies to the Attic base.

The vocabulary or individual elements of the Attic Base and their grammatical role are as follows from top to bottom:
Attic Base

fillet – separating
torus – binding
fillet – separating
scotia – separating/prone
fillet – separating
torus – binding

The composition manifests principles of harmony, rhythm and dominance. Let’s break it down:

All three fillets are the same height creating a harmonious relation. Also, the tori are both perfect half rounds although by being of different scales they avoid monotony.

The two middle fillets combine with the scotia to provide contrast against the tori establishing a rhythm of binding, separating, binding. The scotia is slightly prone allowing the bottom torus to be larger.

The two tori definitely dominate the overall composition, firmly establishing the Attic Base as a binding moulding.


This post is obviously a brief review of a very involved study refined over thousands of years. However, even a basic understanding of vocabulary, grammar and composition will allow anyone to ‘read’ and appreciate many of the great architectural works of Western civilization.

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Contributed by Patrick Webb 

Wednesday, June 5, 2013

The Renaissance and Baroque

The Alhambra
During the European Middle Ages plaster would continue as a craft but was largely diminished as an art. With few exceptions the prevailing Romanesque and Gothic architecture principally utilized stone both for construction and ornamentation. However, by the Late Middle Ages a significant societal shift was underway. The Moors had established themselves as the dominant cultural force on the Iberian Peninsula. Islamic architecture, which originated a decoration based on an interlaced geometry of the infinite as well as a formalized depiction of natural vegetal forms, “the Arabesque”, culminated in triumphant fervor with the completion of the great Alhambra palace in the 14th century. The prominent artistic medium was plaster.

The magnificence of Islamic art certainly did not go unnoticed in Western Europe. It perhaps served as the final impulse for the Early Renaissance dawning in the Republic of Florence at the close of the 14th century. The Florentines looked back to a glorious Imperial past drawing inspiration to reassert their own cultural values. One Florentine family in particular, the Medici, established a unique liaison between wealth, power and patronage of the arts.

The High Renaissance in Rome

Domus Aurea
Towards the end of the 15th century the rich and powerful Cardinal Giovanni de’ Medici of Florence funded excavations of the newly discovered Domus Aurea or “Golden House” of Emperor Nero in Rome. The 17-year old prodigy Raphael and his 13-year old assistant Giovanni di Udine received the Cardinal’s patronage and were granted unfettered access to the excavations, allowing them opportunity to study the epitome of Hellenistic luxury. Awaiting them in the grottoes were perfectly preserved, highly ornamented plaster panels framing bas-relief grotesques, candelabras and arabesques, all modeled in “stucco duro” lime plaster, as well as myriads of exquisitely realized frescoes depicting mythological histories.

Vatican Loggia

Cardinal Medici, now Pope Leo X, extended Raphael’s commission to decorate the loggias of the papal palace of St. Peter’s, which were then under construction. Concurrently, Vitruvius’ architectural treatise of the 1st century, De Architectura, which included a book on manufacture and application of lime for stucco and buon fresco, had significantly influenced Raphael’s contemporaries Leonardo Da Vinci and Michelangelo. According to Vasari’s account, Giovanni di Udine uncovered the ancient stucco duro formulation and took the lead in the ornamentation, while Raphael focused his considerable talents on fresco. Their teams of apprentices would diffuse the resurgent art of plaster to northern Italy and eventually the entire European continent.

The Late Renaissance in Venice

Venice had a basis of power and wealth nourished by a flourishing trade with the East, separate from that of Rome and Florence.  Venetian architecture was influenced by Byzantine and Islamic themes, and the Venetians were slow to fully adopt the resurgence of the classical forms typical of the High Renaissance. However, after the sack of Rome in 1527 a number of stuccoists and fresco artists found employment among the wealthy patrons of the Veneto region. Together with painters, they established the “Venetian School” and created a distinctively Venetian classical style.

Villa Rotunda
Andrea Palladio was perhaps the most influential architect of the Renaissance who achieved the purest expressions of classical design. Apprenticed as a craftsman of traditional stone carving he extensively utilized plaster as a medium for architectural expression. Palladio’s Villa Rotunda near Vicenza is a signature example of symmetry and articulation of the Ionic order; the exterior being completed with lime stucco. Similarly, the interior was finished with lime plaster and adorned with beautifully modeled ornament and buon frescoes. Palladio would become a case study, an ideal example of an architect who had apprenticed in a trade and possessed a tactile understanding of craftsmanship. His numerous masterpieces were not just the result of his individual genius but also of the cooperation he engendered between himself, the patron, and respected artists and craftsmen who both contributed to the design and executed the work.

The German Baroque

The first stirrings of the Baroque began in Rome. Architects like Bernini felt the best of Roman classical design had been explored, understood and recreated, and were eager to push its boundaries. The result was a distinct stylistic departure that could be best described as exuberance. Formal panels, symmetry and bas-relief gave way to flowing, unbounded ornamentation in alto-relievo. Strong yet lightweight, easy to sculpt and affix, plaster excelled like no other medium in conveying the dynamic vigor of the Baroque.

Rohr Abbey, Bavaria
The conflict arising from the Protestant Reformation of the 16th century culminating in the devastating 30 years war hindered artistic development of the High and Late Renaissance in Germany until the first half of 17th century. The Church, quick to understand the emotional power of the Baroque style, increasingly dictated its inclusion in the architecture of the period. The Baroque, reached its zenith in Germany as an architectural manifestation of the Counter Reformation. It was a determined architecture bearing the message of the grandeur of the Church. The focal point of the great Baroque cathedrals was always above, heavenward. Floors were plain, walls were relatively unadorned at eye level but the ceilings were transformed into the very archetype of heaven itself and the altar, the Most Holy. The feeling conveyed was one of astonishment and humility. Dynamic volumes, shadow, and suspended angels with hidden armatures manifested a divine reality only possible with plaster.

By the close of the 17th century great societal changes were underway across the globe. The Age of Discovery and subsequent colonization had enriched and empowered an ascendant European nobility. Coupled with the emerging Age of Enlightenment, a dramatic shift of power from church to state was occurring across Europe. In our next article we will explore the history of plaster in the architecture of French Rococo and English Neo-Classical.

Contributed by Patrick Webb