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Bronze horse on display at Adonis Bronze in Alpine, Utah

Bronze horse on display at Adonis Bronze in Alpine, Utah

As part of my unit on the history of chemistry, I wanted my students to experience an ancient art. I have written before that, in my opinion, there were three major threads that led to modern chemistry: Greek Matter theories (more on that in my next post), Alchemy, and Artisans. Some of the art forms and technologies invented during Roman and Medieval times are still practiced today in essentially the same fashion, such as stained and blown glass, ceramics, sword making and blacksmithing, jewelry, weaving and fabric dyeing, and some types of metallurgy.

Hoop Dancer, a bronze statue on display at Adonis Bronze

Hoop Dancer, a bronze statue on display at Adonis Bronze

We have some newer tools and a better understanding of how matter works, but in many cases the old techniques haven’t changed much. For example, a glass blower from the Middle Ages would have no problem working in a modern workshop. We have better heating sources for the glory hole and annealing oven, can use a blowtorch to keep areas hot, and have substituted wet newsprint for the smelly leather they used to use. But that’s about all that’s changed.

Blacksmith statue at Adonis Bronze, made with the lost wax technique.

Blacksmith statue at Adonis Bronze, made with the lost wax technique.

I did some searching and found there were several workshops in our area that do bronze casting using the lost wax technique known from antiquity, with a few modern additions. I arranged for my chemistry and 3D modeling students to tour Adonis Bronze in Alpine on Friday, Nov. 7, 2014.

Sketches of horses by Leonarda Da Vinci in preparation for creating the bronze horse.

Sketches of horses by Leonarda Da Vinci in preparation for creating the bronze horse.

Students were prepared by discussing how the lost wax technique works and giving examples, such as Leonardo Da Vinci’s huge bronze horse for the Duke of Milan, Ludovico Sforza, that was never finished. He had devised a method for making the horse in a single bronze pour, and he drew extensive sketches. He even made a full-scale clay model of the horse which stood 24 feet high. He was collecting the bronze for it when war broke out; the French invaded northern Italy and attacked Milan in 1499. The Duke was forced to melt the collected bronze down into cannons, but the French still won. They used the clay horse model for target practice.

Da Vinci's sketch for how he would pour the bronze.

Da Vinci’s sketch for how he would pour the bronze.

A 1977 National Geographic article on Da Vinci included sketches of the lost horse, and a retired American airline pilot named Charles Dent dedicated his art collection to the project. A foundation was created and an artist named Nina Akamu was hired. She used Da Vinci’s original sketches to create a new plan for the horse. Billionaire Frederik Meijer helped to fund the project, and two full-sized horses were cast in 1999, 500 years after the original was supposed to be done. One is at an outdoor museum in Grand Rapids, Michigan and the other stands outside the racetrack in Milan. A smaller scale version is located in Allentown, PA, the home of Charles Dent.

Completed horse statue in Grand Rapids, MI

Completed horse statue in Grand Rapids, MI

We carpooled up to the foundry and began in their main exhibit hall. We divided up into groups, and I handed out cameras to each group so we could record everything and eventually make a video.

Adonis Bronze foundry in Alpine, Utah

Adonis Bronze foundry in Alpine, Utah

The modern version of the lost wax technique has quite a few steps. First, an original model is built out of oil-based clay over the top of an armature, or wire frame. For larger sculptures, a smaller model is created then scanned digitally into 3D. It is scaled up on the computer, then a physical version is cut out of foam using a 3D milling machine.

Yours Truly being attacked by a dragon. It was modeled in 3D on a computer and cut out of foam with a milling machine at Adonis Bronze

Yours Truly being attacked by a dragon. It was modeled in 3D on a computer and cut out of foam with a milling machine at Adonis Bronze

Sometimes the foam model is all that is needed. For example, at last summer’s Fantasy Con in Salt Lake City, a 30-foot tall dragon was built out of foam pieces and assembled and painted. The dragon was designed and cut here at Adonis Bronze. They also made large swords and shields and other display pieces, some of which were in the hallways here.

Foam milling machine used to cut the pieces for the dragon.

Foam milling machine used to cut the pieces for the dragon.

Once the original model is done, it is coated in a silicon rubber gel to make a negative mold. That gel, colored blue, is coated in plaster to reinforce it.

Clay sculptures used as original molds for the bronze statues.

Clay sculptures used as original molds for the bronze statues.

A reddish-brown colored wax is melted and kept bubbling in vats. It is scooped up with metal pitchers and poured carefully into the silicon mold to coat the inside and make a thin layer. The final bronze statues are usually not solid, as that would take too much bronze. They are usually less than ½ inch thick.

Balboa Bars - vanilla ice cream dipped in melted chocolate and dipped in nuts or sprinkles.

Balboa Bars – vanilla ice cream dipped in melted chocolate and dipped in nuts or sprinkles.

The flexible silicon is then pulled away from the wax positive. Any imperfections are fixed and wax cups and sprues (spouts or channels) are added to direct the flow of the bronze to all parts of the mold. The silicon molds are stored for future use in case extra copies of the statue are needed.

Clay model for Wingless Victory statue.

Clay model for Wingless Victory statue.

To create another negative mold that will hold the hot bronze, the wax positive is dipped into a thin ceramic slurry which coats the outside and inside of the hollow pieces. The slurry-coated wax is then dipped in sand. The sand pot has air blown up through it so that the ceramic slurry can be quickly inserted and coated.

Silicon rubber mold for Wingless Victory

Silicon rubber mold for Wingless Victory

It’s kind of like making a Balboa ice cream bar at Balboa Beach in southern California. There, a chocolate or vanilla ice cream bar (like the wax positive) is dipped in a chocolate coating, then immediately dipped into nuts or sprinkles while the chocolate is still liquid. Here, the wet slurry is dipped into sand, then dipped into liquid cement and allowed to dry. This ceramic/cement negative mold is hard enough to withstand the hot bronze without cracking. Vents are also added so that air can escape as the bronze is poured in.

Vats of melted wax ready to pour into silicon molds.

Vats of melted wax ready to pour into silicon molds.

The molds are placing upside down in an oven and heated to melt out the wax, which is collected and re-used. This leaves a hollow area for the bronze. The molds are then placed into a kiln and heated to the temperature of the molten bronze, about 2100 ° F (1200 ° C). The bronze is melted in a blast furnace inside a balanced crucible. The bronze casters wear thermally insulated suits and carefully pour the bronze into the heated ceramic/cement molds.

Pouring hot wax into the silicon rubber mold.

Pouring hot wax into the silicon rubber mold.

Once the bronze and molds cool, the mold is broken off and the bronze pieces are “chased” – the cups and sprues are cut off along with any extra bronze that might have leaked around the edges of the mold.

Removing the silicon rubber from the wax positive.

Removing the silicon rubber from the wax positive.

If the statue is large and made from separate pieces, the pieces are then assembled together using welding torches and metal staples. Sandblasters are used to smooth the seams and staples so the surface appears continuous.

Wax mold after chasing, with the halves of the mold combined and cup and sprues (distribution channels) added.

Wax mold after chasing, with the halves of the mold combined and cup and sprues (distribution channels) added.

To get the right finish and colors in the bronze, the statue is sent to a room where chemicals (acids, bases, finishes, etc.) are added to create a desired color. Sometimes the color is created by heat treating – the bronze, which is an alloy of copper and tin, will take on a range of purple and red hues simply by heating areas to just the right temperature with a blow torch. The final coloration is called a patina. The surface is then waxed to preserve it from oxidizing.

Coating the wax with a ceramic slurry to make a negative mold.

Coating the wax with a ceramic slurry to make a negative mold.

The final step is to add a base, usually of wood or marble, then prepare the statue for shipping and display.

Coating the slurry in sand. Air blown up through the sand to make it easy to coat the slurry.

Coating the slurry in sand. Air is blown up through the sand to make it easier to coat the slurry quickly.

It was a fascinating tour. I asked many questions, and got some great things on tape. They were not doing a bronze pour today, so at some point I need to get back to videotape that. They were nice enough to give me a packet of photos showing a statue of a woman going through the entire process. I scanned the photos and created a Powerpoint slideshow, which I am linking to here: Adonis Bronze slideshow-s

Cement-sand-clay slurry casts with wax inside. Notice the sprues that distribute the bronze once the wax is melted out.

Cement-sand-clay slurry casts with wax inside. Notice the sprues that distribute the bronze once the wax is melted out.

I am amazed at how many of these steps haven’t really changed from Da Vinci’s time (or earlier – some examples have been found in Israel that date to 3700 BCE). He did not have silicon rubber to make the negative mold from the clay, and so a direct technique was used. A core of clay was dipped in wax and the wax carved into a final shape.

Melting the wax out of the mold. This is the

Melting the wax out of the mold. This is the “lost wax” step. It leaves a hollow for the bronze to fill.

Sprues were added and the whole thing buried in a compacted sand pit with drains in the bottom. The wax was melted out by heating the sand from the sides or underneath, leaving a clay core supported by rods and a hollow negative space surrounded by hot sand. The bronze was then poured in, allowed to cool, and the whole statue dug out and filed and polished to its final shape. How Da Vinci would have accomplished this with a 24-foot high horse is beyond me.

Pouring the molten bronze into the pre-heated ceramic/cement molds.

Pouring the molten bronze into the pre-heated ceramic/cement molds.

At some point I hope to find a way to duplicate this process on a small scale using pewter or another alloy with a low melting point. I know small heated crucibles are available to melt pewter. Now all we need is a way to re-create the lost wax technique to make the molds.

Assembly of the Wingless Victory statue. Large pieces are welded and stapled together, then smoothed and sandblasted to remove seams.

Assembly of the Wingless Victory statue. Large pieces are welded and stapled together, then smoothed and sandblasted to remove seams.

Perhaps we can carve the sculptures out of wax and coat them with plaster-of-Paris, then melt out the wax. We would have to be careful to not dehydrate the plaster. Or perhaps the molds could be made with wet clay and fired, then filled with metal. It would be a challenging project. If anyone has done something like this, please let me know.

Acids, bases, metal salts, and heat are used to create different colored patinas on the surface.

Acids, bases, metal salts, and heat are used to create different colored patinas on the surface.

Wingless Victory on display in the showroom at Adonis Bronze

Wingless Victory on display in the showroom at Adonis Bronze

Feather dancers, a statue on display in the showroom of Adonis Bronze.

Feather dancers, a statue on display in the showroom of Adonis Bronze.

An elk and Mark Twain. Notice the differences in the patina colors on the elk.

An elk and Mark Twain. Notice the differences in the patina colors on the elk.

Other clay statues. They are built around a wire and metal rod armature.

Other clay statues. They are built around a wire and metal rod armature.

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My summer this year was mostly taken up with astronomy related activities. I flew on SOFIA (see my other blog: spacedoutclass.com) and took an astrobiology workshop at the Great Salt Lake to study extremophiles in June, then spent most of July writing up my experiences and archiving the SOFIA video clips. But during the first week in August, I did return to chemistry and the elements as I participated in a materials science workshop offered by ASM, the materials science association of America (yes, I know, the acronym doesn’t fit. It used to be the American Society of Metallurgists, but has grown to include all material sciences, so now it’s just ASM International). I had heard of these workshops before, and this is the first time they’ve been offered in Utah. When the announcement went out from the Utah State Office of Education, I signed up immediately.

Weber State University campus seen from the science building

Weber State University campus seen from the science building

The workshop was held at Weber State University in Ogden. I couldn’t attend the one at BYU because I was in Palmdale flying on SOFIA that week. Even though it was a bit of a drive to go up to Ogden for five days, I did manage to carpool the last three days with two other teachers from Utah Valley, and we had some good conversations while driving up and back. We met at the Park and Ride at Thanksgiving Point each morning. One was a middle school science teacher in Alpine, the other a Technology teacher at the Nebo Learning Center in Springville. Other teachers in the workshop ranged from chemistry teachers (and a WSU chemistry professor) to industrial arts teachers doing Project Lead the Way. Getting to know the other teachers is always a highlight of attending these workshops.

Teachers in the ASM Materials Science workshop at WSU

Teachers in the ASM Materials Science workshop at WSU

The course was taught by Becky Heckman, who teaches materials science courses at an International Baccalaureate school in Princeton, Ohio outside Cincinnati; and by David McGibney, a teacher from Sammimish, Washington. He was also a finalist in the original Teacher in Space program. A third teacher, Chris Miedema, from Ottawa, Canada also helped out as an ASM trainee teacher. All three have been through these workshops before and have received additional training to present them, traveling to several locations each summer for a week at a time.

Weber State University chemistry lab, with Dr. Donaldson and his wife.

Weber State University chemistry lab, with Dr. Donaldson and his wife.

The course was divided up into sections by the types of materials, with an overview on Monday. We looked at the properties of metals, ceramics, glass, composites, and polymers and alternated our time between in-class discussions and demonstrations and lab activities. We were in the current WSU science building (a new one is being built) and used the chemistry lab upstairs. Some of the labs I’ve done before, such as the activity series of the elements, but we did them in new ways or from different perspectives. Most of the labs will be directly useful in my chemistry class this year. A few use equipment that will require some grants to get, such as a small kiln for raku pottery that runs about $800. They provided some starter materials, such as a bag of sodium polyacrylate and some metal electrode kits, that were given by various chemical companies.

Testing the Reactivity of Metals in Copper Sulfate Solution.

Testing the Reactivity of Metals in Copper Sulfate Solution.

Workshop Highlights:

Activity Series with Copper: We used plastic bottle performs instead of test tubes to test various metals in a solution of copper sulfate, then observed the differences in reactivity. This is a variation of the Activity Series of Metals lab, but is presented as an excellent inquiry/discovery lab. I’ll use this during my second semester as we talk about reactivity and reaction types, leading into my lab on copper compounds.

Borax glass beads. The green beads are on nichrome wire, the blue beads on copper wire.

Borax glass beads. The green beads are on nichrome wire, the blue beads on copper wire.

Borax Glass Beads: We had two types of wire, nichrome and copper, bent into small loops. We heated up the loops in a torch flame, then dipped them into a cup with borax powder, then heated it again, until a bead of vitrified borax formed in the loop. The nichrome bead was green, the copper wire bead was blue. It took some practice not to get too much borax on the loop, so that it didn’t drip into the torch burner.

Metal Activities. From Bottom clockwise: A penny squished through a stretching machine, tin and bismuth alloy buttons, tin splotches and shreaking tin, pennies turned to "silver" and "gold."

Metal Activities. From Bottom clockwise: A penny squished through a stretching machine, tin and bismuth alloy buttons, tin splotches and shreaking tin, pennies turned to “silver” and “gold.”

The Alchemist’s Dream: We did a variation on the old “turning copper into gold” lab that didn’t require pre-1982 pennies (which were made of pure copper). This one uses a solution of zinc powder and sodium hydroxide, just like the other version, but deposits the zinc onto the copper using electroplating. A zinc electrode is in the solution is attached to the positive lead, and the penny is placed inside a plastic spoon with holes in it and touched with a copper wire attached to the negative lead. The zinc appears instantly. It is less dangerous than heating up the zinc-lye solution, and the zinc layer is more even, producing a better-looking golden penny when heated up on a hot plate. I’ve already done this lab in my chemistry class this year with excellent results.

Playing with starch and water solution at the ASM camp.

Playing with starch and water solution at the ASM camp.

Thixatropic vs. Dilatant Solutions: We did the old cornstarch and water oobleck lab (outside, as this is very messy) but looked at it from the perspective of thixatropic (adding shear force or shaking makes the solution less viscous, such as shaking a catsup bottle) versus dilatant (pronounced “die-laa-tant”), where shear forces make the solution more rigid, such as the starch-water solution. These are both examples of non-Newtonian fluids.

Making sulfur allotropes. We did this outside because of the smell.

Making sulfur allotropes. We did this outside because of the smell.

Sulfur Allotropes: Heating sulfur flowers until it turns orange, then carefully pouring into water produces a rubbery form of sulfur. Depending on the temperature and how quickly it is heated, sulfur has several allotropes. We also produced sulfur crystals.

Crystal Bead Boards: Taking a DVD case and filling with small plastic beads, then taping it together to make a single layer. These beads can be shaken to illustrate crystal lattices and imperfections, such as linear cleavage planes, vacancies, etc. Mixing two colors of beads or even two sizes of beads can show substitutional and interstitial alloy structures.

Sir Ken Robinson TED Talk: A very provocative and inspirational talk on the nature of learning and education that all teachers should watch (all students for that matter). Here’s the link: http://www.ted.com/talks/ken_robinson_says_schools_kill_creativity.html.

Annealing, Quenching, and Tempering: We heated bobby pins and paper clips (having different levels of carbon in the steel) and tested how easy it was to break them after they had been annealed, quenched, and tempered. Then we learned the differences in crystal structure. A good introductory discovery lab, with inquiry, that I had never seen before.

Tin splotches, made by dripping melted tin onto a steel plate.

Tin splotches, made by dripping melted tin onto a steel plate.

Tin and Bismuth Alloys: We made a series of buttons of different percentages of tin and bismuth metals melted together. We then tested their melting points to see where the eulectic point (alloy with lowest melting point) was. This was at about 58% bismuth to tin.

Steel Wool in Vinegar: We placed steel wool in a small Erlenmeyer flask with vinegar and salt water, then placed a balloon over the mouth of the flask. We measured the temperature of the solution every ten minutes with a laser thermometer (I had never seen these before – pretty slick!) We were asked to predict what would happen with the balloon – would it inflate or deflate? We also did a corrosion lab with steel wool in water, salt water, hydrogen peroxide, and a combination and compared reaction rates.

Polyurethane foam mushrooms colored with food coloring.

Polyurethane foam mushrooms colored with food coloring.

Thomas Thwaites video: A Welsh man received a grant to see if he could build a toaster from scratch, based on a quote from Mostly Harmless, the fifth book in the Hitchhikers series by Douglas Adams. Arthur Dent, who seems to have trouble hanging onto his towel, has landed on a primitive world where he assumes he will soon be in charge due to his advanced 20th century scientific knowledge. He soon discovers, however, that he doesn’t even have the skills necessary to build his own toaster. He can barely manage to make a passable sandwich. Thwaites decided to put the idea to the test; he took apart a toaster and catalogued the parts, then collected all the raw materials needed to build one himself. He had to melt the metal (which he got at an iron mine), create the plastic (he used potato starch, but snails ate it, and British Petroleum wouldn’t give him a jug of crude oil. He finally had to “mine” the plastic from a garbage dump), and he eventually got a crude toaster that lasted a few seconds before burning out. Here is the link to that video: http://www.ted.com/talks/thomas_thwaites_how_i_built_a_toaster_from_scratch.html.

Plastics Labs: We made polyurethane foam plastic, both rigid and flexible. We also made large clothespins, shrinky dinks (plastic cups painted with Sharpie pens, then melted in a toaster oven), a latex ball (although mine looked like a brain more than a ball), and a homemade Styrofoam shape from a mold and polystyrene pellets.

Shrinky dinks. The disk on the left was a #6 recyclable plastic cup colored by Sharpie permanent markers, then heated in a toaster oven. It shrank down to its original size before plastic forming.

Shrinky dinks. The disk on the left was a #6 recyclable plastic cup colored by Sharpie permanent markers, then heated in a toaster oven. It shrank down to its original size before plastic forming.

Making Models of Composites: We created “diving boards” out of foamcore wrapped with tape, then tested their elasticity and Young’s Modulus. We also made “hockey pucks” from cement mixed with plastic Easter grass as a reinforcer, then dropped the pucks from different heights to compare reinforced vs. non-reinforced concrete. The reinforced cement held up to stresses and did not shatter as the non-reinforced cement did.

Bending a large pipe at the CBI plant. The glowing band is where the pipe is heated by electric current induction, then bent by the machine at right. Water is sprayed on the already bent portion to prevent over bending.

Bending a large pipe at the CBI plant. The glowing band is where the pipe is heated by electric current induction, then bent by the machine at right. Water is sprayed on the already bent portion to prevent over bending.

Tour of CBI Pipe Bending Plant: On Thursday, we carpooled over to a subsidiary of CBI Pipe and Supply in west Ogden that bends large pipes for oil or gas pipelines. The pipes are manufactured straight, but there are times when pipelines have to bend, so this company does the bends. The pipes are extruded and heated using electrical current at a very thin line as a large machine pulls the pipes around at a specific angle. Except for the thin band of heated pipe, the rest is cooled with a water jet. We were shown all through the plant, including how the pipes are tested for strength and shear stress in a lab, how they are annealed in an oven, and how they are painted. Some of the pipes we saw being bent were four feet in diameter.

Testing metal samples from the original pipes to determine strength, elasticity, etc.

Testing metal samples from the original pipes to determine strength, elasticity, etc.

Raku Pottery: This was the most complex thing we did, but also the most interesting from a chemistry perspective. We used a special type of ceramic clay, with higher sand content than usual, to shape small pinch pots. A small 120 volt electric kiln was purchased for this workshop, and the pots were fired in it during the first two days. Then we put glazes made of metal oxides onto the bisque ware and fired it to 900°. On Friday, as our final activity, we took the pots out of the kiln while still hot and placed them into new paint cans filled with shredded newspaper. As the pots hit the paper, it burst into flames. The lid was then placed on the paint can to smother the flames. As the oxygen in the can is used up, the flames pull oxygen away from the metal oxide glaze, reducing it back to a metal. The pots come out with metallic shines. I experimented with various glazes and layering colors on top of each other. My best results were with red copper oxide, tin oxide, and silver oxide glazes. Chromium oxide stayed green and cobalt oxide stayed blue. Tin started pink but turned silvery. Copper went from pinkish to coppery metal, and silver from bluish green to silver-white.

Removing the glowing red Raku pots from the kiln.

Removing the glowing red Raku pots from the kiln.

These were just a few of the things we did over five days. The workshop has already been extremely useful for me, and I plan to incorporate more of the ideas and activities into my other courses this coming semester. We received a large booklet with lesson plans as well as a DVD. Perhaps I will even propose a semester-long materials science course for next year at Walden School. We ended the workshop on Friday with a nice banquet at the student union building at WSU and were addressed by a colonel in the Air Force at Hill Air Force Base, one of the cosponsors of this workshop.

Some of the finished Raku pots. Mine is on the right. It's not as nice as others because I experimented with layering glaze colors.

Some of the finished Raku pots. Mine is on the right. It’s not as nice as others because I experimented with layering glaze colors.

Raku pot using copper oxide glaze, which reduced to a copper metal shine.

Raku pot using copper oxide glaze, which reduced to a copper metal shine.

Teachers at the ASM workshop banquet, Friday, August 9, 2013.

Teachers at the ASM workshop banquet, Friday, August 9, 2013.

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