Holiday How-to: Chocolate Leaves

My mom was a chemistry and home-ec teacher, so I grew up in a home where ingredients were carefully measured and food items were attractively arranged. While I got to help out in the kitchen as much as I wanted, I always liked being in the kitchen around the holidays. There were always new tricks or special touches added to dishes and along with these came short science lessons on why we were doing things that particular way.

One of my favorite things to help with in the kitchen were chocolate leaves. When done correctly, these are perfect little molds of the living leaf, just like the perfect molds and casts in the Morian Hall of Paleontology.

A chocolate leaf is made by smearing melted chocolate onto a leaf and putting it into the fridge to harden. Sounds easy, right? It is pretty easy. Read on!


Activity: Chocolate Leaves


Leaves (*See note in step 1.)

Chocolate candy melts

Parchment or wax paper

A cookie sheet or plate for your leaves to rest on as they cool


1. Pick your leaves. I like to use slightly waxy leaves so you don’t have to worry about fuzzy bits in your chocolate. NOTE: Learn about the plant you are picking leaves from before you decide to use them. Many household plants are decorative but poisonous.  Oleander is a great example of a plant that is pretty but poisonous. If you hate botany or don’t know about the Internet, getting pre-packaged basil or mint from the grocery store is a safe way to go. These leaves will be a little less firm, so you will need to be more careful with them.

2. Don’t pick leaves from poisonous plants. Seriously.

3. Wash your leaves with soap and water, rinse them thoroughly and then dry them completely. The chocolate won’t stick to wet leaves, so don’t rush this step. You will only be frustrated.

4. Put wax or parchment paper on a cookie sheet or plate. You want this to be something that will fit in the fridge with no problems.

5. Get out your candy melts. The melts come in a hundred colors. We are using chocolate colored ones in this tutorial. There will be instructions on the package on how to melt the specific brand of melts you purchased. In general, you will put the melts in a microwave safe bowl and microwave them a few seconds at a time stirring as you go. Don’t overheat the melts. They get gross and there is no coming back from that.

6. When you have everything melted and creamy, hold the leaf by its stem. I like pinching it between my thumb and index finger and then using my middle and ring finger to support the leaf. Do what feels comfortable to you.

7. Dip your stirring spoon into the chocolate. Use the BACK of the spoon to spread the chocolate on the leaf. Make sure the chocolate is thick enough that it won’t break when you try to peel it. Place the leaves on the parchment as you work, and don’t let them touch.


8. The side of the leaf you use is up to you. If you are using mint and you put the chocolate on the back of the leaf, you will have some crazy patterns.  If you want something more subtle, use the front of the leaf. Coat the leaf almost to the edges. If you go too far, you will get ugly edges that are hard to peel. But don’t worry! Those leaves are the best to eat.

9. Put the tray of leaves in the fridge and wait a few minutes.


10. When the chocolate is set, peel the leave off the chocolate. You should have a perfect little mold of your original leaf. This may take a little practice. Work quickly as you have something designed to melt with heat in your hot little hands.

11. Done! You can store the leaves in the fridge until you are ready to use them. If the leaves got soft when you were working with them, put them back in the fridge to firm them up. Once they are firm, you can toss them in a plastic container.


Okay! So what’s the science here?

The word “chocolate” comes from the Nahuatl word Xocolatl for “bitter water,” referring to its original incarnation as a hot, spiced beverage in the Mayan and Aztec traditions. Traditionally, chocolate is a mixture of cacao powder, cocoa butter, and a sweetener. To make chocolate palatable and stable, we now mix milk solids, added flavors, modifiers, and preservatives.

Those candy melts? NOT CHOCOLATE! In this example, they are sort of chocolate colored, so they have that going for them, but they also come in a bunch of colors that are not known to nature so… not chocolate. They are mostly made of sugar and vegetable fats – not cocoa butter – and depending on the brand, they may throw in a little wax for better melting. Mmmmm… wax.

The advantage to the melts over the regular chocolate is that they do have the wax and the vegetable oil in them, which makes melting easier since the chocolate doesn’t need to be tempered. It hardens pretty quickly and sticks to whatever you dip in it, so it makes a great coating for cake pops or whatever crazy things show up on Pinterest this month.

Want to get super nerdy about your chocolate?  (I assume you do…) MIT has these tidbits available.

What’s in typical chocolate?

  • 10-20% cacao
  • 8-16% milk solids
  • 32-60% sugar
  • 10-20% cocoa butter
  • 2% theobromine and polyphenols

Cocoa Butter Chemistry

Fats and oils are organic molecules made up of three fatty acids chemically linked by an ester bond to glycerol. Fats are solid at room temperature, while oils are liquid.

Cocoa butter fats are made up predominantly by three major fatty acid molecules: Palmitic Acid, Stearic acid, and Oleic acid.

Oleic acid is unsaturated (has a double bond on its carbon chain), making it kinked and unable to pack well with other molecules. Because of this, a greater portion of oleic acid in the fat results in a lower melting temperature for the cocoa butter.

Chocolate makers can adjust the amounts of each fatty acid to produce a chocolate that melts only in the mouth, giving it a superior quality.

Tempering chocolate

The cocoa butter in chocolate can have several different crystal structures (three-dimensional patterns in which the fat molecules pack). There are six known chocolate crystal forms, or polymorphs. You can obtain each form by varying the fatty acid ratios and the temperature at which the chocolate is tempered (cooled).

Only a few of the polymorphs are considered good for gourmet chocolate because they give the right blend of snap (when you bite into the chocolate) and melting (when it warms up in your mouth). Melting is especially important because it controls how well the chocolate disperses and releases flavor onto your tongue.

Whether you will be constructing culinary masterpieces this fall or sitting back and enjoying the kitchen creations of others, we hope you have a happy holiday with you and yours!  (And when you’ve had a little too much togetherness, we will be open on Friday…)

Ecoteens build model artifacts for Block Party, opening soon

by John Pederson and Marce Stayer

The Aztecs, one of the greatest Mesoamerican cultures, had all the hallmarks of an advanced civilization. One of their most famous structures, the Templo Mayor, graces the Aztec portion of the John P. McGovern Hall of the Americas. It is a fantastic temple complex, the main religious center of the Aztec capital, and is a feat of architectural genius.

Aztec pyramid complete!

A true-color version of a model Templo Mayor will grace the demonstration shelves of Block Party, HMNS’s new interactive exhibit. And it was built by Moran Ecoteens

The Houston Museum of Natural Science is building a new exhibit called Block Party inspired by the materials used in the construction industry. Curated models of exhibit hall pieces (and visitor-submitted ones) will be on display at the new exhibit. So when the Moran Ecoteens were presented the task of making some of them, an Aztec temple was a popular choice. An image of a temple as inspiration was printed out, and we were ready to build…or so we thought.

John and Connor constructing the pyramid

John and Connor solve building support problems while constructing the pyramid.

Turns out, not all toy building blocks are useful for this purpose. And after we grabbed enough bricks to make the first two exterior layers of the temple (e.g. the Step Pyramid at Saqqara has six “layers”), it was all we could do to prevent the third level from collapsing under its own weight. (To save bricks, we had only built the outside of each layer, leaving the inside hollow.) Eventually, over the course of several days, I worked out a system of struts, columns, and crossties to hold the layers together; the hollow inside was now full of scaffolding. This allowed us to construct a model with accurate dimensions, while reflecting realistic building techniques. The Aztec temple walls were stone encased in painted plaster; our temple reflects this with rigid supports enclosed by a decorative outside shell.

John P. and Aztec pyramid 2

John stands with his model Aztec pyramid built from plastic blocks.

Our multicolored model is the prototype of a future model of the Templo Mayor. The new one will be made of realistically-colored bricks and have a simpler brick-laying scheme, more similar to the Aztec inspiration. Hopefully, those who see it will appreciate both the spirit of the Aztec culture and the engineering genius that defines the monument.


Cream of the Science Crop: Becoming an Ecoteen

You might be wondering how you can get involved doing cool projects for the museum like the Block Party demos. Here’s some information and application advice directly from Marce Stayer, director of the Ecoteen program.

The Moran Ecoteens are the museum’s teen volunteer program, open to teens ages 14 to 17 and rising ninth grade through rising 11th grade. Teens may apply beginning in December by sending their contact information to Stayer. You’ll be asked to provide your name, street address, a phone number and an email where they can be reached. The first week in January, information packets and applications are sent out to all who apply. Applicants will be asked to include a résumé, a letter of recommendation from a current teacher and an essay on the teen’s favorite area of science. The essay can be related to artifacts in our permanent exhibit halls, but it doesn’t have to be. If you’re interested, work hard to write well! We always receive more applications than slots available for this very competitive program.

Completed applications are due Feb. 28. As applications are turned in, teens are invited to schedule an interview. The process must be complete by the second week in March.

Dimetrodon skull and skull

Ecoteens built this model Dimetrodon skull for Block Party, as well.

Selected teens are required to volunteer for one two-week session during the summer. Xplorations summer camp runs on a two-week-on, one-week-off schedule and Ecoteens may choose from these two-week sessions. A new Ecoteen is required to volunteer in the classroom as his or her first assignment. At the end of each week, the teen’s performance is graded by his teacher and turned in to me. If his performance is satisfactory, the Ecoteen may volunteer for additional weeks and have opportunities to work in other areas.

In addition to classroom assignments, Ecoteens are trained to work the touch carts and permanent halls throughout the museum and some are allowed to work in the Special Exhibit halls. They are trained by master docents from the adult volunteer guild for these assignments. They also give science demonstrations to the classes during camp sessions. We have movable demos in Chemistry and Physics, we have a catapult and trebuchet demo, and this past summer, one of the Ecoteens wrote a biology demo called “Microscope Safari” and another created a Morse code demonstration.

Lastly, the Ecoteens help the Youth Education department by working on various crafts that are used during camp — wands and hats for Wizard Academy, belts for Star Warriors Academy, plaster footprints, teeth and claws for the various paleo classes, giant T. rex footprint cut-outs, complete skeletons made out of paper bones, and whatever the classes need. We also write and perform the CSI crime scene on Fridays and put on the Wizard Academy Triwizard tournament. In short, we jump in wherever we are needed!

If this sounds like something you’re interested in, now’s the time to ask for an application so you can get started and be competitive. Best of luck!

Editor’s note: John Pederson is a Moran Ecoteen Coordinator and high school student. Marce Stayer’s official title is Director of the Moran Ecoteen Volunteer Center.

13 Freaky finds at HMNS

Tentacles, bodies and skeletons, oh my! No matter how beautiful or how vital to the history of natural science and life on Earth, some things are just a little freaky. Check out this short list of our top 13 strange, weird and scary artifacts housed in the permanent halls of the Houston Museum of Natural Science.

13. Stone hands


Sculptor Harold van Pelt carved this hand from a solid block of a special mineral. The sculpture is an exact replica of his wife’s hand.

12. Stone skull


Pelt also carved this, a life-sized replica of the human skull, identical to the real thing inside and out. That includes the brain case. The jaw is removable from the skull.

11. Cambrian sea creaturescreep09

They’re soft and squirmy and have strange, meat-eating mouthparts. These guys aren’t around anymore, but you can get up close and personal to these models based on fossils discovered in Cambrian rock layers. Watch a CG video of them swimming in action alongside trilobites and orthoceras in the Morian Hall of Paleontology.

10. Fossilized sea scorpion pincerscreep06

Sea scorpions didn’t always get this big. But when they did, their claws were brutal! Sea scorpions were the apex predator in the Cambrian seas, with a poisonous stinger and these toothy pincers. These in our collection measure about six inches long. Imagine getting pinched by those puppies!

9. A shark that could swallow an elephantcreep07

Megalodon, the largest shark to have ever existed, could swallow platybelodon, a mastodon ancestor, in a single bite. Good thing they’re extinct, or whole ships might go missing.

8. Stuffed bird specimensCreep02

Our preserved specimens of extinct, rare and modern life can be a fascinating walk through taxonomy and the diversity of life on earth. But they’re still treated skins stuffed with cotton. In these specimens, cotton holds the eyes permanently open.

7. Feeding lion


The glass eyes of this preserved lion seem to challenge all who pass. And the severed leg lets us know he means business. What can you say? Life’s hard on the savannah. Keep it real.

6. Floating model orthocerascreep05

This prehistoric mollusk was an ancestor of the modern squid and octopus. In Cambrian rock, their numerous conical shells make this one of the most successful species of the era. And this model, looming overhead, calls to mind that Lovecraftian god of the apocalypse, Cthulhu. (Click the link for Google images if you’re not cool enough to be familiar…)

5. Wall of skullscreep08Nearing the end of the fossil record we find a who’s who of hominids. Homo erectus, australopithecines and Neanderthals included. But it’s pretty disconcerting to stroll around the corner and be confronted by a skull collection of human ancestors staring you in the face.

4. The mummy of General What’s-His-Name


Better than hominid ancestors are those famously well-preserved Egyptian mummies that draw crowds from around the world. This one was a man said to have been a general of the New Kingdom Pharaoh Thutmose III, dating back to 1450 BC. Now that’s an old corpse.

3. The mummy of Neshkhons


I find it more creepy that we know who this body actually was for some reason. Don’t you? This is the mummy of the noble lady Neskhons, who lived during the 21st Dynasty of Egypt, between 1070 and 945 BC. Like many mummies, she was discovered with her most important organs preserved in canopic jars, not including the brain, of course. To ancient Egyptians, the brain was some worthless head-goop.

2. Disembodied head


This mummified head was discovered with a gold-leaf mask, its eyes painted on the outside looking up to the heavens in a symbol of reverence for the gods. The head dates back to between 200 BC and 100 AD.

1. The Aztec god of human sacrifice

creep01In pre-Columbian Mexico, the Aztec empire stretched for thousands of miles with modern-day Mexico City at its heart. Millions were sacrificed to the god Tlahuizcalpantecuhtli (pronounced tlah-wheeze-call-pan-teh-coot-lee) at the top of the Templo Mayor, the great temple in the middle of the city. Sacrifices were beheaded at the top of a tall flight of steps, and the skulls rolled hundreds of feet down to the city floor. The Aztecs believed the sacrifices kept their food and water plentiful, but the scare tactics also made them the most powerful empire of their time.

Come see the freakshow before Halloween, or come in costume to Spirits and Skeletons Halloween night!


Thank an archaeologist for human history on International Archaeology Day!

On Oct. 17, we celebrate International Archaeology Day. Last year, the Houston Museum of Natural Science participated on a large scale for the first time in a long time. This year, we will have our “Second Annual” version of the same. So what is archaeology and who are these characters that practice the art of archaeology anyway?

Ask anyone and they will answer “Indiana Jones!” when asked to name a famous archaeologist. Hollywood and the media in general tend to gravitate to this entertaining, but totally off the mark, representation of what it is to be an archaeologist.


Archaeologists are people who study the past. They do so with one goal in mind: reconstructing what our ancestors were up to. In the end, while we might find broken pottery, stone tools, or more sophisticated or larger artifacts, what really counts is the answer to questions like these: Who made this? Why? How? How long ago was this?

It takes a special person to be an archaeologist. Patience truly is a virtue. Doggedness comes to mind as well. It won’t hurt to be lucky, but having knowledge will guide you to that breakthrough you’ve been looking for. You’ll need willingness to continue learning, going hand-in-hand with the admission that you really don’t know all that much. All of these are good traits to have.

Luck is part of all this, but the insights archaeologists come up with and share with all of us can be a whole lot more interesting and head-scratching than any Indiana Jones movie. In that regard, archaeologists are like time travelers, our contemporaries who bring ancient cultures back to life, sometimes so much so that you can almost feel it and smell it.

Recently, I’ve been reading up on the presence of early humans in what is now called the Amazon rainforest. My perception of the prehistory of this huge area is changing quickly. Yes, there were early settlers in this part of the world. Paleoindians did reach Brazil, Bolivia, Peru, Ecuador and the Guyanas. Our knowledge of these early immigrants in this part of the world is so small compared to what we know of North American Paleoindians. But… all that is changing, thanks to the determined efforts of a handful of archaeologists, the very same people whose work and insights we celebrate on Oct. 17.

Take Dr. Anna Roosevelt, for example. A professor at the University of Illinois in Chicago and a curator at the Field Museum in the same city, Dr. Roosevelt has been investigating early human presence in the Amazon for decades now. The information she and her team have uncovered now point to an Amazon region that was very different thousands of years ago — well before the arrival of the Europeans. It was so different that these Amazonian Paleoindians would have a hard time recognizing the current landscape, just as much as we have a hard time coming to grips with the existence of large, densely populated settlements in many portions of the Amazon.

Marajo Island - location (2)

Map of Brazil, with the location of Marajó Island.

To get to this point, Dr. Roosevelt and her colleagues worked for years in the Amazon, in places like Marajó Island as well as rivers further inland. Marajó, an island the size of Switzerland located at the mouth of the Amazon River, yielded evidence of densely-populated settlements, occupied for centuries. This research took years to complete in circumstances where creature comfort was sometimes a distant notion. It took perseverance as well, as the new data and new interpretations ran counter to older, more established explanations of the prehistory of the region. Research in the interior relied on the willingness of non-archaeologists to share news of interesting finds on private properties. Sadly such willingness is not always forthcoming, resulting in the loss of an unknown quantity of materials all over the world.

Building trust among the locals and upholding that reputation is not easy. One has to be determined, focused and dogged in the pursuit of knowledge. Dr. Roosevelt’s team checked off all these boxes, and came up with cool finds, some on land, some underwater.

Diving in the Xingu River, 2001

Archaeologist Dr. Anna Roosevelt diving in the Xingu River, 2001.

On International Archaeology Day, we pay homage to the work done by people like Dr. Roosevelt. Local archaeologists, professional and avocational, physical anthropologists, and artists who work on facial reconstructions will all be at HMNS. Museum docents will share their insights and enthusiasm about archaeology with hands-on experiences, pointing to the various halls in the museum where archaeology is covered. These include the John P. McGovern Hall of the Americas, the Hall of Ancient Egypt and the section of human evolution in the Morian Hall of Paleontology. The event starts at 10 a.m. and ends at 4 p.m. Dig it!