The Role of Aggregates and Fibers in Plaster

Rammed Earth
Courtesy of Root Down Designs

Originally posted April 2016 on Traditional Building Magazine Online

“To see a world in a grain of sand and…hold infinity in the palm of your hand.” – William Blake

In my last post, I discussed binders, the “mineral glue” as it were, that holds things together. Now it’s time to consider the “things,” the aggregates and occasionally fibers that typically compose the greater part of the volume and mass of a plaster.

While it’s true that most aggregates and fibers are less costly than our precious binders, they’re not simply cheap fill material. Rather, they play a very active role in the strength and performance of the coating as well as the aesthetic quality of the finish. We’ll approach the subject here by considering various physical properties of aggregates and fibers.

Sharpness

It seems intuitive that if your aggregate is sharp and jagged that it will be easier for the binder to find a “key,” that is to say a means to physically attach. Clays and limes shrink as they dry, threatening to crack or otherwise weaken the plaster. Crushed sand and glass are examples of very sharp aggregates that can help overcome this weakening effect, permitting the application of thicker base coats.
Sharper is not always necessarily better. A disadvantage of sharp aggregates is that they make it challenging to achieve a smooth finish. Often plasterers will switch to a more rounded aggregate such as a river or rinsed sea sand for that final coat. Finish applications are applied relatively thin to minimize shrinkage and the rounded nature of the aggregates allows the plaster to be easily brought to a smooth finish with the trowel. Whether an aggregate is sharp or more rounded can be quickly and simply determined by rubbing it between the fingers.

Granulometry
Another approach to counteract the potential effects of shrinkage is to pay close attention to granulometry, the distribution of aggregates of various sizes within a plaster. Particularly for the thicker base coats it is important to have a small percentage of larger aggregates, a majority of medium size ones and a small portion of fines in the mix. This allows the aggregates to interlock most efficiently with the smallest quantity of binder required to fill the voids. For the thinner coats of finish work a smaller distribution of finer aggregates permits the plasterer to create a smooth, closed surface. Usually a visual inspection in the hand will furnish a good indication if you have a sufficient distribution of aggregate sizes.

Gypsum plaster 1200x magnification Courtesy of Plâtres Vieujot

Hardness

By hardness we’re actually referring to the more interesting quality of softness. Gypsums and certain natural cement binders have the unique and interesting characteristic of being “self-binding,” that is to say they don’t actually depend on aggregates to perform well as a plaster. That opens up a great deal of aesthetic freedom regarding what aggregates can be added to them. Often, softer aggregates such as chalk, porous limestones or crushed gypsum rocks are utilized. It only takes a short while before the binder becomes harder than the aggregates allowing the surface to be cut, sanded or otherwise honed to a smooth surface for a striking resemblance to actual limestone.

Porosity

Silica sand, crushed marble and glass are relatively impervious; however, I personally love the benefits of porous traditional aggregates such as crushed limestone, terracotta and pumice, especially when making lime plasters. I find such plasters more ductile, comparatively smoother to apply. The porous aggregates soak up water like a sponge. They can be particularly helpful for the “grounds” or base coats of fresco work. As water evaporates from the binder it gradually and evenly is replenished from the porous aggregates maintaining the surface at the perfect level of humidity for buon fresco painting, extending the working time significantly.

Density

Being mineral based, most aggregates range from medium to relative high density. However, there are a few exceptional minerals that produce lightweight aggregates. Among these are Perlite and Vermiculite. These minerals have water trapped in their crystalline structure. When heated sufficiently they “exfoliate” or expand dramatically, something akin to a mineral popcorn! The resulting aggregates are correspondingly lightweight, have greater fire resistance and significantly increase the thermal and sound insulation value of plasters made with them.

Traditional lime plastering with exposed stone
Courtesy of Lafarge

Hydraulicity

Certain aggregates create a “hydraulic” or accelerated setting action in lime plasters. We’ll make this family of aggregates, known as “pozzolans,” the focus of its own future essay.


Flexibility

In addition to aggregates, fibers can be a very useful addition to plaster binders. Straw and manure have been used for millennia to help reduce erosion in exterior clay-based earthen plasters. Horse, goat and other animal hairs increase the tensile or flexural strength of gypsum and lime plasters, particularly useful for plasters applied over lath thus subjected to greater shear forces than they would experience over masonry. Burlap woven from hemp, jute, sisal or coconut fibers can be embedded into walls in large webs and are very effective in reinforcing as well as attaching traditional plaster moldings and ornament.

Hopefully this sheds a little light on the importance of aggregates, part of an overall effort to demystify the medium of plaster. In our next essay, we’ll commence our in-depth review of traditional plaster binders with clay, expanding upon its chemistry, manufacture, properties and possible specifications.


Contribute by Patrick Webb

Decorative Plastering

Students at the
American College of the Building Arts

Without question the craft of plastering has always held widespread practical utilitarian value to our built environment. Stuccoes rendered in exterior provide a sacrificial function, protecting vulnerable substrates from erosion and water damage. Plaster applied inside insulates, attenuates sound and provides a sanitary, durable wall surface. Extrusions of profiles in plaster create mouldings that add architectural interest, helping to delineate space by means of shade and shadow. However, among the many craft specializations of the Decorative and Applied Arts, plaster is by far one of the most expressive mediums. We'll take a quick overview of the Art of plastering via some of the traditions still practiced in Decorative Plastering.

Color and Texture

Clay plaster with osyter shells

Fortunately, two of the most commonly used minerals to produce plaster, lime and gypsum, are inherently very white and accept color readily. A few clays are also a light grey and can be tinted to produce a broad, if muted range of colors. Other clays are naturally occurring in a variety of earthen colors such as sienna, umber and ochre that most of us love just as they are.

Marmorino, meaning "little marble", is an Italian tradition of integral colored lime putty plastering inherited from the ancient Romans. Enjoying a 20th century Rensaissance in the Veneto it soon was popularized once again in Italy and now throughout the world.

The French have there own long standing tradition of adding colors and aggregates to plaster. The French plaster is based on gypsum which is naturally more matte than lime. So, instead of marble  the French tradition emulates limestone, called Stuc Pierre, meaning "Stone Stucco". The surface of Stuc Piere is typically shaved with a "Berthelet", a hand held plaster razor, and often scored to create joints in imitation of ashlar masonry. Virtually every culture has developed its own artistic flare using color and texture with plaster: Shikkui in Japan, Tadelakt in Morocco, Enjarre in Mexico to name a few additional examples.


Ornamentation

Moroccan "gebs" or Gypseries

There are two principal approaches to creating ornamentation in plaster. The first is reductive. Morocco has cultivated master artisans of  "gebs", otherwise known as Gypserie, a wonderful tradition of carving into gypsum plaster that is very akin to wood carving, using similar chisels and gouges.

A more widespread reductive method applied to a variety of different plasters around the world is Sgraffito, carving plaster in very low relief. Sgraffito relies on contrast of color between plaster layers for the effect and is a relatively inexpensive way to add a lot of visual punch.

Of course there are the additive forms of ornamentation for which plaster is famous. The finest ornamented stucco is done by hand, in situ. Lime is the preferred medium although sometimes a quantity of gypsum is added to speed up the work and create higher relief. The most awe inspiring work left by the ancient Romans and emulated in the Renaissance was all painstakingly carried out by hand by armies of sculptors. These must have been very exciting times to be a plasterer! As mold making technologies increased in the 18th century, in situ ornamentation became largely displaced by pre-cast ornamentation in gypsum plaster. Gypsum has a rapid set, just a few minutes, so once time has been invested in a master model, many copies can be made quickly.

Enrico Trolese, contemporary Venetian Stuccotoro

Scagliola and Buon Fresco

There are a few really special applications of decorative plastering that could easily take a lifetime to master. One of those is Scagliola. Scagliola is a technique of emulating marble, typically with gypsum plaster. The artistry required is tremendous. Just matching colors as they occur in marble or developing your own color palate is a challenge in itself. As the technique requires cutting, folding and stacking loaves of plaster in various orientations repeatedly, you must continually visualize what is happening inside, how all of those layers are coming together in a natural way, recreating the subtle variegation of color, veining, stratification and fracturing that occur in marble are all separate skills.

Perhaps the highest artistic expression of plaster, one that blurs the line Buon Fresco. Painting mineral pigments into lime plaster while it is still fresh takes incredible understanding of materials. The plaster must be prepared in a way so that it maintains a consistent level of dampness for as long as possible. Fresco can be as simple as brushing two or three coats of a mineral wash into a completed wall to give it a soft, cloudy, parchment effect to most elaborate works of fine art and trompe-l’œil.

What is important to recall about all of these various decorative plastering traditions is that many of them can and are used in combination. Scagliola might be pressed into moulds to make ornamental pieces that resemble carved marble. Marmorino or a similar fine lime putty plaster is the grounds for painting Buon Fresco.

The art of plastering really has not changed much in thousands of years. We use the same commonly available materials and techniques we always have. And although to become truly expert at the various arts of decorative plaster requires patience and practice, the truth is they are quite humanistic endeavors, appreciable and accessible to most everyone.



Contributed by Patrick Webb

Plaster Word of the Day; 11 - 20

ADOBE

The work ‘adobe’ comes directly from Spanish who in turn inherited it from the Arabic ‘al-tob’ (الطوب). The term simply means ‘brick’, having its origins in ancient Egypt as verified by surviving hieroglyphs.

Today ‘adobe’ has a more specific meaning of a sun dried brick formed from clay, sand, water, straw and sometimes having additives such as manure, soil, lime, etc. A similar mixture is used for mortar and as an earthen plaster to bond and protect the adobe bricks.

SCRATCH, BROWN, FINISH

This description of a 3 coat plaster system (usually over lath) is more common in the US and applies to all types of plasters: lime, gypsum, cement etc.

The ‘scratch’ coat is the base layer and as you might guess receives scratches to receive the next coat. It is important that the scratches run horizontal, essentially forming little shelves for the next coat to sit inside and lock into

The ‘brown’ coat is the middle coat. Traditionally either brown sand was used or some mineral tint was added so that the plasterer could easily gauge if he had sufficiently covered the scratch and to make sure he had good coverage when applying the finish.

The ‘finish’ is applied last. Unlike the first two coats where thickness was achieved and the geometry of the wall was established, the finish is typically a thin veneer to create a smooth surface.

Image courtesy of Franco Saladino

MARMORINO

‘Marmorino’ describes an entire system of lime plastering inherited directly from the Romans as recorded by Vitruvius. It enjoyed a vibrant revival during the Renaissance, spreading from the Veneto region, where it had continued as a craft tradition, to the rest of Italy.

The word ‘marmorino’ is the diminutive form of the Italian ‘marmo’, meaning ‘marble’. So ‘marmorino’ has a direct translation something like ‘little marble’. Outside of Venice it has taken on the more specific meaning of the final coats which are rich in lime and taken up to a high polish

Image courtesy of Simple Construct

EARTHEN PLASTER

In discussing Adobe construction a few days ago we mentioned that the bricks traditionally would receive an earthen plaster. Earthen plasters are undoubtedly the oldest form of plastering because no cooking is required. Rather than having a chemical ‘set’ it simply dries out. They are still used in Adobe construction as well as over other natural building substrates such as Straw Bales and Rammed Earth.

The binding component of an earthen plaster is clay, meaning clay is the material that holds the other ingredients (silt, straw, sand etc.) together. A certain percentage of clay is required to make a suitable plaster. Too little and the plaster is weak and friable. Too much and the shrinkage of the clay will lead to cracking.

The image provides a good initial test to see if a site soil has a good percentage of clay or will need to be modified.

FRENCH PLANE

A common tool in the French plastering tradition. Wider versions are used to level wall surfaces whereas the narrow version is the tool of choice for creating faux masonry joints.

The narrow tool is called ‘Chemin de Ferre’ or ‘iron horse’. An appropriate metaphor as the plane has the shape of a train engine and runs along a straight edge or ‘track’.

Image courtesy of Plâtres Vieujot

RUN-IN-SITU

Previously we discussed the running of plaster moulds on a bench to later be affixed. However, a more traditional method is to realize the work on site or ‘in situ’. This type of work is usually referred to as ‘run-in-place’ in the US.

The same mechanical process of running a profile along a track is used for run-in-situ as for bench running; however, the level of skill required is much higher. Instead of using Plaster of Paris which has a rapid set, a common mix is to use lime gauged with gypsum plaster and a small amount of retarder to provide more time to complete the moulding.

Image courtesy of Palladio Mouldings

MODEL

Modeling describes the art of placing enrichments on a moulding in preparation to create a mould. Hence you’ll hear the expression ‘model and mould’ although they are two distinct actions not always performed by the same person.

A good modeler must understand layout well and is responsible for geometric enrichments. However, an experienced modeler will develop at least limited sculptural ability for repeated motifs such as egg-and-darts and acanthus leaves

Image courtesy of Palladio Mouldings

ARCHITECTURAL SCULPTING

There is a distinction made between the responsibilities of the modeler and that of the architectural sculptor. Although still possessing a solid understanding of geometry and precedent in ornamentation, architectural sculpting goes beyond planting repeated motifs on a moulding to embrace free formed, often asymmetrical or unique designs such as cartouches, bas-relief or ornate column capitals such as the Corinthian capital being developed here.

Having been trained classically in figurative study and having worked in mediums as diverse as clay, plaster, wood, stone, the architectural sculptor often assumes the responsibility of art director working with his team of modelers in larger ateliers.      


Contributed by Patrick Webb  

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 14^th 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 14^th 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 15^th 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 1^st 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 16^th century culminating in the devastating 30 years war hindered artistic development of the High and Late Renaissance in Germany until the first half of 17^th 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 17^th 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

An American Couple’s Perspective on French Wine and Plaster Traditions: Viticulture

Château de Chambert

Nature. Culture. Perhaps these seemingly disparate aesthetics were no better reconciled than by the French Renaissance tradition of the formal garden.

“In the Renaissance taste the garden was an extension of the main design. It was a middle term between architecture and Nature. The transition from house to landscape was logically effected by combining at this point formality of design with naturalness of material.” – Geoffrey Scott, The Architecture of Humanism

To this point we have considered Varietals and Terroir…learning about grapes and minerals…exploring soils, weather and geology…recognizing all of nature’s generous contributions. All that we have hitherto discussed is most fundamental; however, wine and plaster are uniquely products of culture. The balance of our five part series will consider the human touch.

Viticulture in Wine

Although located in what is considered the “old world” of wine production, Bordeaux is squarely in the forefront with regard to wine-making technology.  So in this segment we are going to discuss an aspect of the Bordeaux wine industry that receives nowhere near the attention it deserves. We are talking about viticulture. Viti is latin for vine therefore viticulture roughly translates to vine cultivation.  In this article, we will examine two methods of viticulture that are essential to making a great wine; vine manipulation and pest control.

Vine leaves contain chlorophyll cells that absorb sunlight enabling the plant to extract carbon dioxide from the air and convert it to sugar. The nutrients imparted by the sugar feeds the vine roots, grape clusters and leaves ensuring the entire plant receives exactly what it needs, when it is needed.

Allowing too much foliage shields the grapes from the sunlight they need for the last stage of their healthy development, so pruning is crucial to producing a quality wine. However caution must be exercised with cutting, because every cut is an entry point for pests to enter and attack the vine.  On the other hand, if too many leaves are pruned, the plant does not have the means to absorb sufficient sunlight to sustain the entire vine.

Wine grapes emerge at the end of the growing season so the plant’s nutrients must further be shared with the new grape clusters. If there are too many clusters, the sugar and acid levels will likely be undeveloped and/or unbalanced resulting in a poor showing as a wine.  Too few clusters negatively affects potential profits from wine sales.

Pest control is another very important aspect of viticulture. In the 1870s a small, deadly phylloxera louse made it’s way to Europe and all but wiped out all wine production. Phylloxera destroys the grapes, rots the vines and often leaves its larvae in the root, eventually killing the vine completely.  Although Bordeaux and Europe at large have regained their wine producing capabilities, phylloxera and other lice, along with viruses, bacteria, fungi, mites and insects are still among the many threats to healthy vines.

In an effort to eliminate ongoing threats to their vineyards and livelihoods, many late 20^th century wine growers often used chemical fertilizers and pesticides indiscriminately.  Thankfully much has changed since then with most of the region’s winegrowers using more environmentally conscious, natural pest control methods.  For example, Bordeaux wine growers are currently and constantly experimenting with root grafting in order to find the genetic combination that is naturally resistant to harmful bacteria and viruses.  Scientists and wine growers are also experimenting with sea algae as a natural deterrent to gray rot. 

There is no doubt that viticulture is both science and art.  Winemakers must have intimate knowledge of their vineyard’s terroir as well as which viticulture methods will work best within its parameters. It is with this intricate knowledge and dedication to quality that winemakers are able to extract the best wines from the best grapes.

Viticulture in Plaster

France is a geologically, minerally rich country. Correspondingly rich in culture, the French have been very successful in exercising their influence over a number of raw mineral materials to produce some of the finest plasters in the world. The plaster equivalent to Viticulture is baking. Let’s now take a closer look at how 3 minerals are prepared for our blended plaster, Terre de Séléné.

Clay is the primary mineral used for plaster in Terre de Séléné. It is an abundant mineral worldwide, the result of millions of years of erosion. In parts of France a relatively pure form is available just under the topsoil, just a few feet below ground. It is easy to excavate and is still traditionally dried by the sun. Later, with minimal effort, it is ground into a powder ready to be used for plaster. While there are a variety of clays in France, clay with a low shrink-swell capacity such as Kaolinite is desirable for Terre de Séléné.

Historically, the French were enamored with this type of clay for additional uses. The word “Kaolin” comes to us directly from French. They in turn inherited the term from China. In the early 18^th century the French were obtaining an extremely pure form of clay useful for porcelain, “China”, from a deposit near a mountain the Chinese called Kao “high”, Ling “hill”.

Gypsum is the secondary mineral used in Terre de Séléné plaster. Gypsum is plentiful in France and particularly so in Paris. Gypsum plaster is almost synonymous with the expression “Plaster of Paris”. Paris in fact sits on a “massif” or deposit of mineral gypsum that is among the largest and finest in quality on earth. Naturally occurring gypsum is a type of salt that precipitates through cycles of evaporation from lime or other calcium compounds, typically in lagoons or inland seas.

Preparing gypsum plaster requires a little more effort and energy than clay. It is usually mined from underground deposits. Relatively soft as a stone, it is easily pulverized to a coarse sand ideal for baking. Most of the gypsum plaster useful for Terre de Séléné only needs to be baked at under 350° F for less than an hour. In general, considerable influence can be exercised in the baking process. Adjustments to the grind, temperature, length of baking and even barometric pressure can produce an amazing range of properties in gypsum plaster such as fast setting plasters good for casting or extremely dense, hard plasters appropriate for floors or countertops.

Limestone is the third mineral used for our plaster blend. In abundance in the South of France, limestone is a sedimentary stone, the result of millions of years of marine skeletons accumulating on ancient sea beds. The lime most useful for Terre de Séléné plaster is very pure, having little contamination from magnesium or silicates. By itself, limestone is very useful as a building material; however, to produce a plaster requires considerable fuel and labor.

Limestone is found underground but is plentiful and easier to extract from surface mines. Much harder than gypsum or clay, extraction is laborious. For baking limestone is broken into golf ball size pieces. Traditionally, it was baked for 24 hours in vertical kilns at an extremely high temperature of 1500° F. Modern production methods utilizing crushers and horizontal kilns have reduced the time considerably.

The resulting “quick” lime is highly caustic, potentially hazardous to handle. At this point of production enough water is introduced to cause a partial reaction that reduces reactivity and danger. The slaked lime, also known as dry hydrate, is now ready to be blended with the clay and gypsum plaster to make Terre de Séléné.

As you have read, the French traditions of Viticulture and plaster preparation are very sophisticated. The usefulness of our modern scientific, chemical understanding still lags behind the practical experience gained through centuries of empirical observation and practice. This is especially evident in our subsequent, fourth segment considering the art of the blend, Viniculture.

This article was coauthored by Angela and Patrick Webb