Thursday, December 31, 2015

Spicing It Up!

The past year of blog posts have hopefully broadened your understanding of how soils are intertwined with our lives. For the international Year of Soils 2015 each month has focused on a theme where soils have been shown to be an imperative part of our lives. We know we must preserve this resource for primary functions and ultimately our existence. However, what's life without a bit of spice (very subtle Dune reference here)? Soil contributes to aspects of our lives such as culture. Part of our culture involves art and, yes, soil is a part of art! Ink for paleolithic paintings (i.e. cave drawings) often used "red" soils for color. Modern artists still use soil in their paintings (see below). Soils also can be used to dye yarn and fabrics. But this earthly material can be used for more than just color in artwork. The soil itself can be used to make pieces of art such as ceramics. This month's post will focus on the particulars of soil used in ceramics for December's theme "Soil and Culture."

One of Janis Lang's soil paintings.
Specifically clay is the type of soil used for ceramics. Soil consists of several different sized particles: sand, silt, and clay. Clays are the smallest of these, but just because a particle is small (less than 2 microns) does not automatically make it a clay. Clay particles have a particular mineralogy or elemental make-up and structure that allows for various chemical and physical properties. One of these is that clays behave as colloids. Existing as a colloidal means when particles are suspended in water they do not settle out due to chemical characteristics. Furthermore not all clays are chemically the same in that they behave differently in regard to chemical reactions that can occur as well as how they interact with water.

Dewatered (dried out) clay of a former salt marsh.

We can see with our eyes the various chemical differences in clays from the color present. A red clay will have oxidized iron, while a grey clay may be reduced iron (Oxidation and reduction refers to the capacity of an atom to accept or donate an electron for those of you interested). A white clay is totally absent of iron. Likewise, the physical property differences can be seen and felt and are a reflection of the arrangement of layers of atoms in the clays. I won't go into specifics, but broadly there are two main groups, 1:1 clays and 2:1 clays. Clays from the 1:1 silicate clay group tend to have less water holding capacity (less shrinking and swelling when wet and dry), less plasticity (as in workability like play-dough), less stickiness and cohesion. This group is also known as the kaolinitic clays. The 2:1 clays have the ability to greatly shrink and swell causing major issues for buildings and agriculture (See Solid Ground post from May) and have greater plasticity and cohesiveness than the 1:1 clays. So why does having different physical and chemical properties matter in ceramics? The point of ceramics in the simplest sense is to mold a clay into a shape and keep it that way. Ceramics use kilns (ovens) to finalize this desired shape of the clay. Different properties of the clay will affect how these shapes will end up in terms of color (prior to glazing), and also affect what temperatures and the processes used to solidify the shape. Combinations of different types of clays as well as other soil particles (silt and sand) can create pieces that have a variety of different properties. The type of piece or use desired will dictate what type of clays (or non-clay materials are needed) to create. For example making a plate would require very different material than a brick.

Mottles of oxidized iron (red) in clay soils.

Clays will solidify when dried. However, only adobe clays are durable when air-dried. Therefore in ceramics, clays must be dried in a kiln. During this process the clay will shrink. The more water a clay holds to greater possibility for shrinking (possibly unevenly) and cracking. How the clay is dried and fired will effect the overall outcome of the piece. This process is typically slow to avoid the aforemenioned issues that can occur even in clays (even those with lower water holding capacity). As the temperature in the kiln increases water is lost through evaporation (100 degrees Celsius) and dehydration (350-500 °C). Above 500 °C the clay has lost water in the interior part of the clay layers and these chemical changes are not reversible. As the temperatures get higher carbon is lost (900 °C) and other compounds are oxidized and lost as well (e.g. sulfates). The final step is "vitrification" where the hardening step occurs. The original chemical structure (i.e. mineralogy) begins to disappear and the elements are fused together in a different pattern. With porcelain, this process occurs completely where the material is totally glass-like in that the original crystalline pattern is lost and in its place one that is not as "organized." You can think about it on a larger scale in terms of quartz crystals versus glass. Many clays begin as a crystal formation and through this firing process become more glass like.

To complete apiece in the ceramic process usually a glaze is applied to provide color and water-proofing. Glazes are a glass finish that is coated over the fired pottery. The glazed pottery undergoes a firing process in the ~600-1400 °C  range, which will depend on the glaze used. Glazes are silica based, but contain other elements that provide color to the finished piece.  Below are pieces that are from various clays and have several glazes used. Glazing temperatures for these four pieces ranged from 1223 °C to 1351 °C.

An example of several ceramics that have various clays and glazes (the finishing color and waterproofing) from Brian Johnstone of Nehalem Clayworks.
From left to right the first four pieces are as follows per Brian Johnstone of Nehalem Clayworks:

1) Wood ash glazed teapot with dark clay body and semi-porcelaneous handles
2) Salt-glazed two-piece iron-rich clay goblet with Rutile oxide slip (liquid clay w/ coloring oxides added) under
3) Dark Celadon-glazed porcelain lidded bottle.
4) Extreme high-temperatutre salt-glazed pitcher with rutile/cobalt underglaze slip.

The complexity of these processes unfortunately cannot be addressed fully in this short blog post. However, two excellent reads (thank you, Brian!) are Ceramic Glazes by Cullen Warner Parmelee and Clay and Glazes for the Potter by Daniel Rhodes (which much of the information presented here was gleaned from). Also, if you are traveling the Northern Oregon Coast be sure to stop by Nehalem Clayworks to see a ceramics studio in action and talk with Brian and Kate Johnstone about their work!

I hope you have enjoyed the the International Year of Soil themed blog posts from this past year. More posts to come in 2016, so stay tuned! As always requests for soil topics that interest you can be submitted in the comments.

Happy New Year from Talus Soil Consulting! 

Monday, November 30, 2015

Soils of Climates Past, Present, and Future

Silently lying under our feet you would never expect soils to hold so much information on our past, present, and future. Soils hold evidence regarding historical climatic conditions, what we are dealing with today, and what we can expect in the future. We can learn from soils about what has happened previously in an area and even what we can expect globally. The International Year of Soils November theme is not surprisingly "Soils and Climate!" This month's blog post will focus on examples of where soils revealed information on our climate over time and what to expect in the future.

Recently, I traveled to Hawaii for a little bit of a break. However, just because I was on vacation did not mean I ignored the beautiful soils surrounding me! All over I found colorful surroundings. These bright red soils are known in the broadest soils taxonomic classification as "Oxisols" (See I'll Take an Order of the Andisol Please for more information on soil taxonomy). Oxisols are known as the most weathered (i.e. modified and broken down) of all the soils. This process is driven by warm soil temperatures and lots of precipitation typical of tropical environments. Hawaii has both of these conditions, so there are lots of oxisols present on the islands!

So, what if I told you that there are oxisols in California? From what you have heard for the last several years, California is in a severe drought. This would be the opposite of tropical, right? How does the state have soils that form from abundant precipitation and warmth? We may not have those conditions now, but the presence of oxisols does reveal that these conditions were in California in the past...waaay past! The Ione formation found outside of Sacramento, California is an oxisol indicating that very different climatic conditions were found in this area once upon a time.
LAWR UC Davis SBGG 2002 Field Tour

Present and future information can be somewhat tied together as we know (somewhat) what is happening currently and can predict what will occur from the current conditions/changes. One example is the thawing of permafrost in the arctic. Currently we are experiencing increases in average temperatures. These minuscule changes (ones that humans can't necessarily detect from day to day) can drastically affect ecosystem processes. The melting of permafrost in the arctic changes atmospheric conditions. How does this happen? Ok, go back to what we were talking about in terms of soil formation. If warm and moist conditions help soil formation what about cold and moist? If an area rarely has water moving through the soil (remember the water is frozen and not much chemical transformation is occurring) or biologically active soil temperatures do not occur very often (i.e. the microorganisms are sleepin' moist of the time due to freezing temperatures) soil formation will be super slow. For example in Alaska, these conditions have created layers of permafrost where soil, both mineral and organic, remain in a state of suspended animation. The soils are storing a high amount of carbon (i.e. dead plants). However, change these conditions by setting this area into defrost mode and we wake up those microbes; a release this carbon in the form of carbon dioxide and methane (i.e. greenhouse gases) occurs. We have plenty of both of these gases helping to keep the planet warm, so this process is not favorable at this time. In this way, soils are letting us know what is happening right now and what to expect in the future.

Melting permafrost in Alaksa causing soil subsidence and road collapse.

Learning from the environment around us can help humans to understand where we have been and where we are going in regard to climate. Soils and climate have an interconnected relationship where they have influenced each other and continue to do so. Continued study of both of these areas can help us to understand, learn from, and possibly prepare for what's next. 

Saturday, October 31, 2015

The House that Soil Built

Over the past year, the Talus blog has focused on soil and its important role in our lives. Topics often discuss soil's indirect involvement in our world.  However, what if you depended on soil directly for your shelter? There are many cultures that have in the past or currently depend on soil to protect them from the elements. This month's International Year of Soils theme is "Soils and the Products We Use" will highlight these amazing structures built from soil.

"Casa Terracota" in Colombia.

Many people who have visited the southwest of the United States are familiar with Adobe houses. These houses are typically soil (15-30% clay) and mixed with an organic material such as straw. The soil/straw mixed is baked into bricks. Due to soil's thermal properties it holds heat and cold well. In deserts these properties are very desirable as temperatures can fluctuate greatly.

In Korea, there are soil houses known as Mokcheon Earth Homes. The name Mokcheon comes from is the village where these homes were first built. In more modern times they are known in the western world as "cobwood" homes as wood is now used to stabilize these structures.

Many of us may remember "sod houses" from our grade school days in the United States. The pioneers who ventured west found that there was a lack of trees on the Great Plains, so they had to improvise. Using sod (grass, roots, and soil) they could build shelter that was well insulated, but fairly damp. These houses did not hold up to frequent rains and constantly required upkeep. European sod homes (developed centuries before the US pioneers) had layers of bark to prevent the roofs from leaking and lasted 30-40 years! These structures can be built into the landscape and have more recently gained popularity due to people's fascination with living like hobbits! Improvements have been made to these homes in more modern times (i.e. rubber to prevent roof leaks). 

hobbit house, green roof, sod roof, sod house, old world, Nordic countries, Iceland, Norway   
Because today is Halloween, the last soil home example is a creepy one, but one that we are all very familiar with. Soil can be our "last home" or final resting place. Countless varieties of earth tombs have been used in cultures around the world. Many of these structures are very well preserved and have protected their occupants very well over the years. These structures have allowed us to understand ancient cultures as well as see how they used soil to honor their dead. 

Greek Tomb -

Monday, September 28, 2015

Burnin' down the house!

Fire season along the West Coast of United States has been pretty amazing this year. Firefighters from all over the world have been flown in to assist with major fires from Washington to California. The massive fires take out buildings and infrastructure in addition to thousands of acres of grasses, shrubs, and trees. However, during these catastrophic events these forested ecoystems are often not totally destroyed. Part of this has to do with soil! For the International Year of Soil's September theme, we will explore how "Soils Protect the Natural Environment" in the context of wildfires in forests.

When forest fires occur, the soil temperature will raise a certain amount depending on the fuel present (amount of burning material), initial soil moisture, and the speed of the fire. In a fast moving fire with moist soils, you can have very little heating of soil. With minimal heating, the seedbank (seeds from plants in the area) can survive and regenerate after the fire. The plants help to reestablish the ecosystem  and improve damage soil properties. These seeds are protected in the soil often for years until some sort of disturbance takes place!

Soil can also protect existing trees if the base or the roots are covered by it.  The tissue that was protected by the soil (organic or mineral) and remained alive can resprout and grow again.  In essence, the tree can go on living. This is seen in redwood forests where the parent tree may have been affected by fire (note: redwoods do a pretty darn good job resisting damage from fire due to high tannin and low resin content). The sprouting and growth of new trees from the base or roots of the parent tree creates what is commonly called a "fairy ring". 

Soils can be severely affected by fires, but their sacrifice fortunately provides protection for the vegetation and seedbank present. This is one of many ways soils protect the natural environment, but one that is quite relevant given the state of our forests in the west!