Two Videos Below:
Video 1- How to make the molding material.
Video 2- How to use the molding material.
Making and molding for duplication is a great way to replicate parts. It is a process that has a very long history and technology has made the molding and casting of many materials possible. And each process comes with some positive aspects and some negative ones. One of the most successful products has been the use of RTV Silicone, a two-part flexible elastomer that can be catalyzed by either a tin or platinum reactant. Mixed 1:1, and poured over the part to be copied, the results are typically excellent. It provides fine detail, de-molds fairly quickly, can be used to cast many times, generally requires no release agent, has high heat tolerance, and it is dimensionally stable. But, the advantages come with high cost, limited shelf life, and of course, it is not reusable. Once you are finished with the mold it is discarded. And urethanes are possibly the next most popular with casting enthusiasts. Despite the vast array of materials, none are really reusable. They are all relegated to the trash bin when they fail to perform satisfactorily or are no longer needed. But, I do have an alternative for your consideration. It is a reusable, inexpensive, and very functional molding material based on gelatin as the elastomer, glycerin as the plasticizer, and water to form the colloidal suspension.
I have been using this molding material for several years and it was initially developed to secure cover slips to microscope slides. At first I used agar, but that was expensive and difficult to find locally. So, I tried gelatin and glycerin and it worked really well. I noticed that when poured on a flat surface, it formed a flexible film that acted like rubber, had a melting point well above room temperature, and could form a mold. So, I used it for small items and general castings. But recently, I decided to try and make larger and more complicated molds and cast with epoxy resin, paraffin wax, polyester resin, and Plaster of Paris. The results are promising but there is still a lot of experimenting to do. But, I think that by posting the process now, some of the readers will be able to add their information in the comments section and we can all work together to make a better process. The basic formula is shown in video 1 and it is very easy to make. Initially, the first time it is formulated, a stovetop is best as continuous stirring is required. It can be made in a metal pan as well as in Pyrex containers or glass beakers. Containers are easily cleaned with hot water. Once the elastomer is made, it can be reheated in the microwave oven using short times until you learn how much time is needed. For small batches, (40 ml), I use about 10 seconds. (In microwave acceptable containers, not metal!). The mix does not require boiling and seems completely dissolved at around 160 Fahrenheit, (71 Celsius). It sets to a rubber-like elastomer at room temperature and remains flexible. Its actual melting point seems to be about 130 F. The flexibility can be varied by using less glycerin for a firmer gel, and more for a softer material. Without using a gelometer, my best guess is that it can vary from about a 15 Shore A to a 40 Shore A, and that compares favorably with Silicone RTV.
In video 2, actual molding results are demonstrated with the advantages and some downsides as well. I recently discovered some commercial products that are reusable but I have not investigated them yet. I mentioned in video 1 that chocolate can be cast as well but that process requires a higher quality glycerin. The material sold in drug stores is not as pure as what is called food grade glycerin. That is 99.9 % pure. It may be available in markets locally, but is definitely available online.
20 milliliters room temperature water.
4 grams unflavored gelatin.
24 milliliters glycerin.
Mix as demonstrated in video 1. I have been using a 10 times batch that is about 450 milliliters. Please enjoy the videos and comment! Ken…
Well, it did work! I used paraffin wax and 1/2 of a red crayola crayon for the color. I did expect the dimension change as that is the nature of wax. I did also chill the mold. So, it is another use for this mold material. Try it!
Photo one is left to right: White LED, UV LED, UV LED with yellow filter. Courtesy: Wikimedia Commons Xofc. Photo two from Proceedings of the National Academy of Science of the US. This site has a complete description and chemistry of the fluorescent character of the banana here.
We are all familiar with the fact that in the fall, leaves begin to change color from green to sometimes brilliant colors, like the red of swamp maples. But, they can also just become brown and fall to the ground. The process is simply the changing of chlorophyll into smaller molecules as photosynthesis ends the life-cycle for that plant for the year. The act of this cell death is called senescence or growing old. The chlorophyll forms catabolites, (smaller metabolites) releasing some energy in the form of fluorescence, but it is generally short-lived and not readily observed. And, the same process occurs in some fruits, like bananas, pears, and apples. But, it has been found that the banana has some interesting differences.
It has been discovered that bananas have different fluorescent signatures as the fruit ages. When green, there is an abundance of chlorophyll and carotene, with no fluorescence. As the banana ripens and become yellow, it fluoresces with a blue color. In fact, the number of days to ripen can be demonstrated by this fluorescence. But even more interesting is the circular patterns caused by cell death which have a distinct fluorescence at 465 nanometers (UV A). Although I have seen these peculiar cell deaths, I was not able to photograph them.
It is always amazing to me that the natural world around us still contains many secrets and the excitement continues when curiosity causes us to look for new and interesting natural processes…
Butter has been a part of the human food sources since very early history. Essentially, butter is made from the milk produced by many different mammals. The dominant basis for butter today is the milk from cows. But, milk from sheep, goats, buffalo, and yaks is common in some parts of the world.
Milk is a water-in-fat emulsion, which simply means that milk and cream contain butterfat in microscopic globules. These globules are surrounded by membranes of phospholipids and proteins. Cream is the portion of whole milk that has a higher level of butterfat that is less dense and naturally rises to the top of milk. This is collected and is the starting point for butter.
Butter is produced by mechanically breaking the membranes surrounding the fat globules and allowing the butterfat to form one continuous solid. The finished product contains free butterfat, butterfat crystals, undamaged fat globules, and water. The composition depends on the manufacture and variability of the starting ingredients. In the video I refer to lactic acid fermentation and that is a common practice in some European countries and the butter produced this way is called cultured butter. In the US the butter is typically not fermented and is called sweet cream butter, and is available with and without some salt added. And although buttermilk is separated out from the butter during the process, most buttermilk is made from fermented skim milk.
The butter that we buy in the store has water contained in the butterfat and varies from about 15 % to as high as 30%. Butterfat as an ingredient is a mixture of triglyceride, derived from glycerol, and several fatty acids. Butter can spoil, or become rancid when these fatty acids breakdown to form smaller acids such as butyric acid which is a pungent smelling and disagreeable tasting chemical.
There is a considerable amount of controversy concerning the use of butter and the substitute, margarine. And although this is not the subject of this post entry, I have a link to the Cleveland Clinic for an overview here
. Let’s make some butter!
Four years ago I had eye surgery, and as a result I now have an annual examination with the surgeon. But, long before I signed up for the procedure I did the research to check the doctors credentials, background, and patient feedback. She is a well respected and patient supported professional so it was really a good choice to proceed with the necessary surgery. And, although I am using my own experience for this post, it is more about the technology and the importance of continuing eye care.
Typically when we go to an optometrist it is with the intention of improving eye sight. But, there is a lot more going on as we will learn. The frequently remembered portion of the eye exam is the test where we look at an eye chart and see how far down the chart that we can read. E, O, M, maybe Z, and in this test called refraction, the optometrist places lenses in front of each eye to determine the best corrective lens strength. This lens correction may be required when the light falling on the retina is either to far or too close due to the eye lens shape. The retina is the area inside of the eye that is like the photo element in a digital camera, or film in older cameras. It contains the rods and cones that allow the light signal to be sent to the optic nerve and provide vision. But, the retina also may contain clues to other problems unrelated to vision. For example, conditions like hypertension, diabetes, melanoma, detached retina and other problems may leave clues that allow the optometrist to suggest further testing leading to early diagnosis of an illness.
This photo is a scanning laser ophthalmoscopy image of a healthy retina from Optomap, a laser device from Optos Inc. Prior to the use of this technology the doctor would use an ophthlamoscope to examine the retina. But, the eye is usually dilated with a chemical to enlarge the pupil so that as much of the retina is exposed to examination as possible. With SLO, dilation is not necessary and the test is fast and painless. But, there are some caveats! This is the first time that I had an SLO done and it was with dilated eyes. So, while I was waiting for the doctor, the images of my eyes was displayed on a computer screen nearby. As I watched the image I noticed what the doctor had called a freckle or nevus. It was a clearly visible asymmetric spot among the capillaries and other features. It has not been a problem and continues to be more of an artifact. Also visible were the "floaters", those dark spots that we sometimes see move around in our visual field. Again, very normal. But, there is some controversy about needing SLO.
This is an Optomap image of a retina showing melanoma as indicated by the small circular satellites in the lower center. These images are presumably fluorescent due to the dilating dye. The controversy about the use of SLO is that it only cover about 200 degrees in the typical 22 mm retina, which is about 72 % of the retinal area. This leaves the edges out of the image where disease can be found. So, I had an extensive conversation with the doctor about the potential use and need for SLO. Particularly important is that insurance may not cover the cost. My doctors take on the subject is that it is a valuable tool as a baseline metric but only as an adjunct to the opthalomoscope
typically used for complete eye examination. So, for me, the takeaway is that we have to be well-informed patients and ask a lot of questions. Any good doctor expects questions and is prepared to explain any procedures. If they are not prepared, perhaps it may not be the right doctor for you. There is a link to this controversy here
. Here's looking at you...
I have had a tree in my backyard for years and have watched the green "seeds" grow and fall each year without knowing what the tree was. The squirrels knew as did other wildlife, but I had never identified the tree and discovered the secrets inside this tree.For me, this is unusual as I am curious about everything and yet missed a great lesson in growing vegetables and flowers. This particular tree is central to a small habitat that I have and use to attract birds and other critters. It has the in-ground birdbath, (See the post on ants swimming), the hummingbird feeder, and the suet feeder for the woodpeckers and other clinging birds. Of course, squirrels also like to try to get to the suet but that is another story. But, it is an area that I have tried to grow several types of flowers including
annuals and perennials. But most failed and I was perplexed to say the least. I had some success with Impatiens and Morning Glories but everything else that I tried died fairly quickly. So, I set out to find out why I was having so much difficulty with this area. And, it all started with this tree in the cover photo.I began by identifying the seed, or in this case the drupe.
(The outer fleshy part containing a seed). I determined that the tree was an Eastern Black Walnut and that it has some very interesting chemistry. Black walnut drupes contain Juglone, (Ju Glone) which is 5-hydroxy-1,4-napthoquinone, yellow quinone pigments, and tannin. The juglone is an alleochemical, a biochemically active material that has an influence on the growth of other living organisms including plants, bacteria and fungi, and even people. Alleopathy can be either positive or negative, and in the case of the flowers I was trying to grow, it was having a negative effect. But, we know that there is what is called "companion gardening" where one plant can be beneficial to another.The area that was not conducive to growth in my case extended from the expanding roots to the drip line of the tree. So, if I had identified the tree sooner I could have saved a lot of time and energy. This is a lesson well-learned.But, that is not the end of the story of black walnuts. The liquid portion of the drupe is brown and stains everything that it comes in contact with and has been used as a dye for centuries. The tannins react with iron and can make a good quill ink. There is a post from the Ohio State University Extension Service on toxicity and some of the plants that will grow with the black walnut tree here. I have also included the following photos of black walnuts in various stages of ripeness as well as the ripe inner edible fruit:
Frequently as we make plans to start a new project or build the next gadget, we have to think about where we will acquire the necessary parts. Some of us already have boxes of stuff around, but, if you are anything like me, they are poorly organized. I know that I have at least one of everything needed but do not know where it is. So, I look around in my list of web sources for the parts and pieces. I began to assemble a list for this page but found a really good site that already had a better wheel. So, rather than reinvent said wheel, I will add a link to the site. Sometimes, it is smarter to buy first quality items, but in many cases, surplus is cheaper and will work as well. But, I use caution as there are times when surplus does not mean cheaper. So be careful when ordering surplus parts. There are some sites I use regularly and can safely recommend but will not endorse. The Electronic Goldmine has been a reliable source with frequently good buys. American Science and Surplus is good for odds and ends, bizarre, and one-of-a-kind items. They also have a fairly good selection of laboratory glassware. But, check the prices! Some are higher than at other sites. Sometimes for electronic projects in a hurry, Radio Shack is a good possibility. But, the prices are high and selection is limited. Electronic kits are also readily available if you like to solder. Velleman has the greatest choice but Carl,s Electronics is also a good choice. They provide the instruction manual in pdf for many products if you want to see how it works first and see the complexity of the build. The site is the property of krkaplan
and he has done a fantastic job of collecting sources. I clicked on several sites and the links are active. It was updated in 2012. Check out the kits section and there are many of the now defunct kit makers like Heathkit and Allied. But, these are an historical perspective and there are modern kit suppliers listed. You can find it here
. A tip of the hat for Mr. Kaplan!
If you only want the instructions for mixing Plaster of Paris please go directly to the video. If you would like to understand more about the chemistry, manufacture, physical characteristics, and some tips for re-enforcing, coloring, dangers, and proper disposal, please read on.
The basis for this post is that I have checked several sites for the instructions and found them wrong, misleading, or lacking in good information about this versatile casting material. Plaster of Paris has been in use for well over 5 thousand years and is still misunderstood. So, while I am not an expert, I have used this material for years with good success and continue to find new uses.
Plaster of Paris is made from calcium sulfate dihydrate, (CaSO4.2H2O), frequently called gypsum. This simply means that there are two molecules of water with each calcium sulfate. It is a naturally occurring mineral found in many locations around the world but was originally named after a large deposit in Montmartre near Paris. The dihydrate is ground and roasted at 150 C (300F) to drive off 1 and ½ molecules of water as steam. The modified material is now calcium sulfate hemihydrate, Plaster of Paris, and has only ½ a molecule of water, 2CaSO4·2H2O + Heat → 2CaSO4·½H2O + steam. Since it takes in energy as heat it is an endothermic reaction. So, when we buy Plaster of Paris, we are buying the hemihydrate of calcium sulfate. In order to make it a castable solid we add water so that it becomes the dihydrate again! The Plaster of Paris gives off the energy that it has stored and when setting into a solid provides an exothermic reaction. It can become very hot and can burn exposed skin. So, it is not used as a casting medium for human parts casting. When it is used as a cast for broken limbs it is used over bandage material and not in direct contact.
Plaster of Paris is a very soft mineral although it can be relatively strong when it is used as a cast. On the Mohs scale of mineral hardness, with talc being 1 and diamond being 10, Plaster of Paris is a 2. This allows it to be sanded, trimmed, and damaged easily. Once set, it is not water soluble, and it has a very low rate of expansion, about 0.1 %. It sets or hardens in a monoclinic crystal lattice which means that the particles are all facing the same direction. This provides a dense cast, but there are still interstitial areas and it is porous.
Plaster of Paris sets in a very short period of time depending on the temperature of the mix and the air temperature. Typically, it can be de-molded in about 30 to 45 minutes. If it is cool to the touch it has at least set. But, set time is not the same as cure time. In order to fully cure, the cast will usually take between 48 and 72 hours with good ventilation to allow any excess water to escape. There is a great deal of speculation on the web about increasing set time. I have seen everything mentioned from baking powder to vinegar. But, adding other chemicals will change the material characteristics and may lead to failure due to interruption of the crystal lattice. The best methods to increase the working time is to use cold water, use short mixing times, or by using an excess of water. It is also possible to purchase Plaster of Paris with retardants that are designed to increase working time. But, by using cool water, and short mixing times, I have had material that had a working time of 30 minutes.
Plaster of Paris can be strengthened by using glass fiber, gauze bandage, or other suitable material. In fact, there is a product called modrock that is coated with plaster and simply moistened to use. It is also easy to color the plaster with poster paint or tempera. But, use caution as some colors can cause an almost instant set time. Food color would be a poor choice as it is not color fast.
Plaster of Paris is a fine powder and should not be inhaled. Pour material slowly and use a mask if you feel the need. But, it is a safe material with great casting potential. One serious caution is to dispose it as the solid and not put it in a drain as it will clog the pipes.
If there are any facts that I failed to include please use the comments section to ask questions or add any other useful information. Now, let get mixing!
These electronic bug killers have been around for some time in various configurations. They first appeared as a smaller paddle and several were made in this country. Now, they are bigger and cheaper, and made in China. And, with the lower cost comes some cautionary suggestions. Despite the fact that it is fun to electrocute nasty flies and other pests, these bug zappers are not toys. They can be dangerous and particularly for children and anyone with a heart condition. These devices are high voltage, low amperage circuits that are poorly made and can provide unexpected and unpleasant shocks. Trust me on this fact! I have taken several of these apart and the circuits vary, but the soldering is very shoddy. If you want more information search for "voltage doublers" or "electronic bug zapper circuits". I have posted photos of some of the high voltage boards and one of the flash tube camera flash. But as a final note, please exercise caution and also avoid destroying the pollinators like bees and other beneficial flying critters. We have already lost too many. And now, on to the video:
Thermochromic materials are those chemicals that exhibit a color change with temperature. The two best known methods of temperature induced color change involve either liquid crystals or leuco dyes
. And, although there are inorganic compounds like titanium dioxide and zinc oxide that show color change with high heat, they fail to be useful as consumer products. A good example of liquid crystal color change is in the “mood ring” which was popular in the 1970’s and is still sold today. These rings are based on cholesteric liquid crystals that change color in the range of temperatures found in the human body. When I was actively involved in chemistry I was able to develop a method of detecting breast cancer with these materials. The technology was based on the fact that cancer cell colonies are warmer than the surrounding tissue and could be seen as hot spots. But, mammography was being developed that was much better than my crude approach.
But, the chemical reactions in this video are based on leuco dyes. These are chemicals that have two distinct color phases. The color change can be triggered by pH, solvent action, or other chemical mechanism. A good example is that of crystal violet lactone, a leuco dye. If it is blended in a microcapsule with dodeconal, a solid alcohol with a low melting point, the alcohol will liquefy, protonate the lactone causing a change in pH, and that will result in a color shift. However, this is a bit of a misnomer as color change due to pH is actually called halochromism
! But convention and culture continues to call it thermochromism. The advantage of these chemicals is that a wide range of temperatures can be fabricated with this technology. The two that are demonstrated in the video are triggered at 86 Fahrenheit. I bought these at Solar Color Dust but there are a number of suppliers that can be located by searching “thermochromic pigments”. They are a bit expensive but still interesting to work with. Enjoy…
This is a bit of a departure for me in that it is rare to go this far back in time. It is a video sponsored by Chevrolet in 1940 and it is essentially selling the 'NEW" light technology. But what I found interesting is the discussion about ultraviolet and infrared light that was just on the cutting edge of technology. What you will find is the the fact that there are corrections to be made based on a look in the rear view mirror but still entertaining. It is also politically incorrect but not for 1940. Sometimes a look back gives us an appreciation for what seems new and relevant. The video is from the Prelinger Video Archive and is in the public domain. Enjoy a look at the past!