Using Scratch Holography in the Middle School Science Classroom

Timothy R. Coughlin
Buffalo State College
PHY 690
Dr. Dan L. MacIsaac

Abstract
	This paper reports how scratch holography was used by a NYS middle school science teacher in their physical science classroom, as well as how scratch holography can afford science teachers a unique opportunity to make overarching connections between light and matter by introducing an inquiry based physical science lesson in their middle school level classroom.  Such a lesson can aid a science teacher in unifying themes and processes in their year-long plan for their students, consistent with both state and national science standards.  
	William Beaty’s Science Hobbyist website is used as the primary source for the design of the presented lesson, as well as for troubleshooting within the lesson.

	

	I wanted to present a lesson that would allow my students to reflect on prior knowledge, make connections between thematic topics, and partake in tangible activities where they could engage in processes of science and gain operational knowledge.  Holography seemed like the perfect opportunity to allow my students to focus on the connection between matter and light in a first hand way.
	Holography is a technique that allows the light scattered from an object to be recorded and later reconstructed so that it appears as if the object is in the same position relative to the recording medium as it was when recorded.  The image changes as the position and orientation of the viewing system changes in exactly the same way as if the object were still present, thus making the recorded image, or hologram, appear three dimensional. Holography is one area that has become an exciting avenue for educators to use for their students to learn due to recent reductions in cost of lasers, film and chemicals.  However, my school budget did not allow for me to purchase enough material for me to give each student their own hologram. Did this mean that they are not afforded the opportunity to allow their students to experience holography first hand?  According to Bill Beaty, no. 
	William Beaty, a researcher at the University of Washington, started a website in 1995 entitled Science Hobbyist, that now boasts nearly 20,000,000 visitors since its inception.  While the site links to numerous scientific topics of discussion and education, the one link that caught my eye was entitled “Draw Holograms by Hand” (http://amasci.com/amateur/holo1.html).  What Beaty proceeds to describe are holograms produced by scratches to a solid surface, or scratch holograms.  This was a phenomena he stumbled upon while walking through the parking lot and noticing a three dimensional hand floating from scratches in the hood of a car left from a towel or buffing mitt.  To recreate this holographic effect, only a piece of plexiglass, or polycarbonate sheeting, a pair of dividers and sunlight were necessary.  In fact, Beaty recommends using the styrene back of a compact disc case.  
	It was clear that I could demonstrate holography to my seventh graders without the worry of chemicals or lasers.  Not only would this method allow for me to design unifying lesson that would encompass multiple topics discussed in the year, but it would be cost effective enough for everyone of my middle school students to produce their own.  However, I didn’t want a gimmick to fill time.  While my goal was rooted in curriculum, I wanted to be sure that the activity could fit as well.  The lesson can be specifically linked to content performance indicators in the New York State Intermediate Science Curriculum.  
	4.4b Light passes through some materials, sometimes refracting in the process.  Materials 
	absorb and reflect light, and may transmit light. To see an object, light from that object, emitted 
	by or reflected from it, must enter the eye.
We would be using a material medium that could absorb and reflect sunlight, in a specific geometric pattern such that the emitted light from the plastic sheet could only enter the eye in a specific way to produce an image.  Photons of light could easily reflect off or transmit through a plexiglass sheet, so therefore scratch holography was a beautiful example of light and matter interacting.  
	Such a lesson could be used to discuss energy, the nature of light, optics, and the interaction of matter and energy, and therefore could fit into the yearlong, holistic plan of a teacher to unify conceptual and procedural scientific themes by providing an avenue for students to integrate personal experiences with their understanding of the world around them, consistent with the National Science Education Standards.  Also, the applications of the technique can easily make the lesson interdisciplinary.  The geometric translation of an image roots application in mathematics, while a business or marketing class may discuss scratch holography in advertising.  Also, the aesthetics of scratch holography can easily be explored in an art classroom.
	I purchased two  48” x 36” sheets of clear Lexan (polycarbonate) from a local hardware store. Using a table saw, I cut them up into 4” x 3” pieces, but many hardware stores will do this for you for free, or a minimal cost, if you aren’t able, or comfortable enough, to use a table saw. My students keep marble notebooks in my science class for lab activities, review questions, and free writing.  I passed out a polycarbonate piece to each student had them tape the corners of the Lexan onto a clean page in their notebooks.  At this point, all students were equipped with the materials, but I thought that just telling them about scratch holograms may be too abstract.  Instead, I showed the video of Bill Beaty and his scratch holograms from YouTube.  The video is only a few minutes long, but shows a variety of scratch holograms of varying complexity being shown with sunlight.  After viewing the video, my students were extremely enthusiastic to make their own.  
	Below the Lexan piece, I had my students draw the image they wanted to scratch.  Most wanted to try the first initial of their name, while others wanted to try shapes like stars and hearts.  The students then proceeded to place the pencil tip on a single point of their image.  Then, holding the pencil in place, they tilted the compass at about a 45 degree angle and made a light scratch across the Lexan with the metal tip of the compass.  They moved around the entire image with their compass, individual point by point like pixels in a digital image, and transcribed corresponding scratches into the polycarbonate sheet.  We then traveled outside and viewed the holographic images in the sunlight.  Some students laid their holograms on the ground and varied the backgrounds behind the sheets, using dark colored binders and black construction paper, to get a better quality image. Others  held their products in their hands and tilted the Lexan until they were able to see their images.	
	Being that not all of my students own dividers or compasses, I borrowed a class set of compasses from a math teacher in my building.  While compasses with pencils in one end are not ideal for the activity due to the sliding of the pencil, they still worked to achieve the desired effect and were cost effective.  My student’s made sure to secure the pencil very tight and have a very sharp tip.  They used the pencil end to mark the points on their images, and used the pointed end to make their scratches.  What would be more ideal is a pair of dividers, or a compass with metal tips on both sides, to make the most precise scratches and to avoid the slipping of the inserted pencil.  Beaty also recommends this on his site.
	I had made a few scratch holograms on my own and each had taken me between 30 and 45 minutes to finish.  Since my class periods are only 40 minutes long, I anticipated that a single class period was not enough time for my students to finish properly scratching their image, so I told them we would continue the following day.  However, I found that there were a few students in each class that came by my room during study hall periods to continue working, and still others worked to finish their scratch holograms at home to show me the following morning.  It was exciting for me to see my students excited about doing science, as well as taking ownership of their personal hologram.  We used these completed examples as demonstrations at the start of the following class.  Those students that finished helped their classmates or tried making a second scratch hologram with the leftover scraps of Lexan I had in the room.  I am fortunate that my room is next to an exit door that opens to an athletic field.  Through out the period, we traveled quickly in and out of the room, testing the scratch holograms in the sunlight, making observations and comparing the quality of the images from one to the next.  At the end of the period, all students had completed their scratch holograms to varying degrees, and were troubleshooting how to perfect their techniques.  Many side discussions ensued amongst students concerning the different types of materials that may work to produce a similar image, as well as “painting the plastic black to see if more light would be attracted to it and make it brighter.”
	The next day, I asked my students a simple question: “What happened to make their holograms work?”  I wrote this on the board and began the class by having them answer this question independently in their journals for the first few minutes of class.  Many students very confidently began writing immediately, while others sat for a moment.  My students understand very well that free writing in their journals is a risk free process, so I found that very few students tried to proceed without some explanation.  I can foresee this having different outcomes, or many more students not attempting to write or even guess, if a teacher has not established that routine in their own classroom.  
	Next, I had them break out into small groups of 3 or 4.  They discussed their reasons amongst themselves, sharing what they wrote down.  It was interesting to walk amongst the groups hearing the various evidences and inferences being argued.  Some students would only argue what they saw, while others tried to extrapolate based on discussions we had previously had in preceding classes.  I did not interfere, or question in any of these groups.  
	Finally, I told each group to take a whiteboard and dry erase markers and sketch out how they believed the holograms worked.  I have found white boarding to be a tremendous instructional tool when employed in the classroom. I gave each group a limited time of 6 minutes to accomplish this task.  Once they finished, we sat as a class in a large circle, while each group presented their whiteboards.  I facilitated the discussion, using a “Socratic” line of questioning in order to differentiate between observations and inferences.  We highlighted common ideas on each of the boards, and focused on subtle differences that made boards more descriptive than others.  The answers varied from group to group, but the ideas of “reflected light,“ “light refracted from the scratches,“ and “light bouncing from the scratches to my eyes” were the most common pervading ideas from class to class.  I facilitated the discussion to have my students make judgments on what inferences had the most support to explain what they observed.  Our class discussions seemed to dwell on specific phenomena that my students observed.  The fact that the image seemed to move as they changed their position brought up a lot of discussion, as well as how the image seemed to flip when you turned the Lexan upside down.  Beaty demonstrated this in the video, and this was a point that fascinated my students when they were able to recreate the effect with their own scratch holograms.
	As with many lessons, while well planned and executed, I would be remiss to say that it went perfectly.  Since each student was creating their own individual product, each student could take individual ownership of the finished product.  However, this also means there were a variety of problems that needed to be examined if a student’s scratch hologram did not come out successfully.  I found that if students failed to produce a holographic image in their abrasions this was primarily due to two reasons, both of which related to how the scratches were made.  
	First, students would make too few scratches.  Just as in a digital image that is blurry due to lack of pixels, two few scratches resulted in an image without detail that appeared as described by one of my students as “a white smear.” In some cases, students were able to go back and make additional scratches to represent the points on their image and have better results in producing their image.  Other times, students made scratches that were too deep.  In this case, the light reflecting from the surface would bend at different angles, disrupting the phase relationship of the light waves necessary to produce the image.  I found students did this most often if they pointed their compass points directly into the Lexan, rather than at an angle, or if students did not clearly see a scratch, in which case they would retrace the scratch over and over again.  The holograms that were the most clear and detailed consisted of many fine scratches over the surface of the glass.
	Other issues usually stemmed from a failure of the equipment.  The success of the image transcription into scratches is dependent on producing scratches that directly relate to specific points on the image being transcribed.  If students did not anchor down the Lexan securely to their notebooks, the distance between the image and the abrasion could change if the Lexan slid, thus causing scratches to be made that did not coordinate with the image and producing the “white smear“ effect as was the case when the phase relationship was lost when the scratches were too few or too deep.  On the other hand, if the compass was not secure at its pivot point, or the pencil too loose, students often tried to compensate by making deeper scratches, or the over stretched scratches produced a distorted image, elongated similarly to looking at the image as if it were in a funhouse mirror.
	Beaty makes a point of addressing different problems that may arise when creating a scratch hologram in the Frequently-Asked Questions link on the page.  I found this extremely helpful to read over prior to the lesson, so that I could anticipate errors that students may be making.  It was very user friendly as he lays out the page as responses to questions he has received concerning scratch holography since first posting his video on the internet.
	I do not suggest directing middle school students to Bill Beaty’s website to carry out the activity on their own.  While the site may be school appropriate, it links to public forums that may not be appropriate.  I found that the site is better served as a resource for the teacher as an instructional aid.  The step by step method of producing a scratch hologram is detailed and accompanied by illustrations, but the specific scientific concepts discussed behind holography are beyond the reading capability of most middle school aged children.
	In conclusion, scratch holography provides a very engaging, enriching, and economic opportunity for children of any age to practice science in a very tactile and real way, that allows for a broadening of scientific understanding consistent with both New York State and National Science Standards.  William Beaty’s personal website is a primary resource for teachers interested in employing such a lesson in their own classroom as a unifying concept and real world application.