Tag Archives: resin

Monday Link-o-Rama

Welcome to the first full work week of September! I’ve been away all weekend, so enjoy these articles and sites:

The Art of Manliness has a nifty guide on sharpening your edged tools. It deals mainly with knives and axes, but it covers a lot of the basics.

Once you’re finished sharpening your tools, you can find out why your teenager can’t use a hammer. The decline of shop and industrial arts classes are leaving even the most basic of manual jobs with a dearth of skilled young workers.

Air and Space Magazine has a nice little gallery of Vietnam War—era Zippo lighters.

I recently came across The Clubhouse, an online community for model-builders, sculptors, and collectors. It seems to be a good resource for help and information on working with plastics and resins, as well as painting and weathering.

Some Confusions in the World of Plastics

I’ve been researching the wide world of plastics for the book I’m working on. I’m trying to make sure my terminology is correct, and it’s proving daunting; plastics is a world where many terms can refer to the same thing, and common-use terms may not be technically correct. Add to the mix a bunch of trade names which are used generically, and you end up with one big confusing mess.

Take urethane rubber for instance. If you are into molding and casting you may have used it. “Urethane” in this case is a shortening of “polyurethane”, the same kind of plastic you use as a clear varnish among other things. “Urethane” is also a specific substance in the world of plastics; it is known as “ethyl carbamate”. Polyurethane does not contain ethyl carbamate, nor is it made from it.

Rubber can refer to a material or a substance. The substance, sometimes clarified as “natural rubber”, has historically been derived from the latex tree, though the proliferation of latex allergies has led to some companies experimenting with different plant sources. Synthetic rubbers, such as nitrile, do not contain latex; the “rubber” in their name refers to the fact that their properties mimic natural rubber. Technically, they are all referred to as “elastomers”.

Thus, “urethane rubber” contains neither urethane, nor rubber.

Speaking of latex, we all know and love latex paint for painting houses both inside and out. Sometimes we even use it to paint props. It does not actually contain any latex. It refers to paints which use plastics as their binders, such as acrylic, polyvinyl acrylic, styrene, etc. Vinyl resins are cheaper than acrylic resins, and most house paints contain a lot more vinyl than acrylic, which is why pure acrylic paint is a lot more expensive than house paint.

In case you are wondering, the acrylic in paint is the same acrylic found in sheet form, known commonly by trade names such as Plexiglas and Lucite. Crazy!

Review: The Prop Builder’s Molding and Casting Handbook

The Prop Builders Molding and Casting Handbook
The Prop Builder's Molding and Casting Handbook

In Thurston James’ second book, he tackles the subject of molding and casting for prop makers in more detail. The Prop Builder’s Molding & Casting Handbook guides you through the most common materials and methods used in many prop shops. Because of its specific focus (and better organization), this book is far more successful than his previous Theatre Props Handbook, which, as I mentioned in my review, meandered through disparate topics with no way to quickly find information.

Though written in 1989, the methods described in this book still hold true today. Though the range of materials we can use today have grown dramatically, they remain improvements and new formulations to older materials whose predecessors can be found in this book.

It remains one of the most widely recommended books for molding and casting props because of the unique niche it fills. It describes the most common materials and methods used in props shops and by hobbyists; these materials are used because of their cost, ease of use, availability, and proven results. Books on molding and casting for manufacturing and industry are more focused on specific or specialized materials, and they aim for a level of consistency and cost efficiency which the prop artisan would never possibly need. Shaving a tenth of a cent off the cost of a casting makes a difference if you are casting ten thousand pieces, but it will be impossible to notice if you are only making ten.

James seems to have had an epiphany in shop safety between this book and the last, as he now presents clear and accurate safety precautions in the beginning of the book, and continues to reiterate them throughout. In his Theatre Props Handbook, safety precautions were nearly nonexistent.

The book does a good job of covering the generalities of mold making and casting. It discusses the model and its preparation, and defines a number of necessary terms, such as undercuts, release agents, mother molds and the like. It describes the considerations of making a mold of your specific piece, and breaks the various molding materials and casting agents into categories. In a way, it describes the process of choosing your materials in an almost flowchart-like manner. If you know what your model looks like, and you know what kind of properties and appearance your castings need, then you can narrow your choices of mold material and casting material down to a few choices. In the book, he describes over thirty of these material choices.

The bulk of the book is used to guide you through the specifics of working with each of these materials. Specifically, he talks about plaster, alginate, latex rubber, and silicone rubber (RTV) mold-making. The casting materials he describes include latex, neoprene, papier-mâché, Celastic, fiberglass (GRP), hot melts (such as wax, plasticine, hot melt glue and hot melt rubber, breakaway glass, thermosets (specifically polyester resin), water-extendable polyester, and urethane. He also has a section on casting with hardware store products, like caulk, autobody filler, water putty, and several others. Finally, the last section of the book describes vacuum forming and how to construct a vacuum forming machine.

It’s Friday. Take a break.

I’m in North Carolina visiting my wife and talking to her classes about being a props person (she teaches scenic design at Elon University). So enjoy the links below and have a Happy Halloween!

Still looking for Halloween decorating help? Check out the Haunter’s Digest forums and the Haunt Forum.

The Craftster forum has a good summary of the different types of resin available to the artisan.

Finally, here’s a tutorial for a cool armor mask.

Have a good weekend!

Choosing the right disposable glove

First, I wish to offer a caveat; I don’t write much about safety, because it’s a highly complex area, especially once you start talking about safety around chemicals. I’m not an expert, and if you are in a workplace situation, there are actual regulations, standards and laws that need to be followed. The last thing I want is someone’s sum total of knowledge about safety coming from “Eric Hart’s Props Blog.” Still, the home hobbyist may not know where to look for information, and the prop shop employee may not know what questions to ask their employer, or what their employer is responsible for providing. Thus, what follows is not a guide for choosing the right disposable glove; rather, it is a guide to what questions to ask and what information to look up to learn which disposable gloves are best for each situation. All the safety data in the world is useless if we don’t know what information we are trying to find, or even that we need to find certain kinds of information. Often, we don’t know what we don’t know.

Dozens of companies make disposable gloves, offering hundreds of combinations of materials, thicknesses and liners. You need to find the permeation data for the specific gloves you are using. This will tell you how long it takes for specific chemicals to work their way through the glove and onto your skin.

No single glove will protect you against every chemical. There were approximately 50,000,000 chemicals registered by the CAS on September 7, 2009, with more being added at the rate of twenty-five per minute. Luckily in theatre, we only use a small percentage of those chemicals. If you work at a theatre or shop in the USA that employs ten or more people (that’s counting the whole theatre, not just the prop shop), then it is subject to OSHA regulations, and your employer is required to inform you of any toxic chemicals you may be using.

As a general rule of thumb, you should be wary of rules of thumb when it comes to safety. But a good rule of thumb to follow in safety is “don’t get stuff on you, and don’t breathe anything that isn’t air.” Choosing the right glove falls under the “don’t get stuff on you” part of the rule. Gloves are necessary because many chemicals can be absorbed through the skin. Chemicals commonly used in prop shops that can be absorbed through the skin include solvents and epoxies. Solvents don’t just include pure solvents like acetone, xylol and mineral spirits, but also any product that includes solvents: spray paints, cleaners, adhesives, etc.

Another good rule of thumb is that latex gloves don’t stop any chemicals. They can keep your hands dry, and they’re great for keeping blood and other bodily fluids from getting on your hands. They’re also useful for the reverse: keeping your own sweat and oils from getting onto your work surface. But as far as working with any sort of industrial or household chemicals, they may as well be invisible.

Notice how I mentioned household chemicals above. Just because you can buy something in a grocery or drug store doesn’t make it safe to work with without proper protection. For example, many cleaners like Windex, 409 and Simple Green use a chemical called 2-Butoxyethanol. The toxic exposure level of 2-Butoxyethanol is less than that of acetone and hexane, placing it in the category of “highly toxic” chemicals. When you start looking at permeation charts for popular glove brands, you see a trend; latex gives you no protection, while neoprene and vinyl will offer only several minutes before exposure begins. If you are using anything other than nitrile, you are exposing yourself to a highly toxic chemical.

If you are using a glove and the substance is splashing or spilling onto your bare arm, it defeats the purpose. Make sure you are wearing sleeves that offer similar chemical protection, or use longer gloves.

Many chemicals we use for prop making are toxic through skin absorption. An example is any of the two-part epoxies we use: sticks of epoxy putty, five-minute epoxy glue, epoxy coatings for fiberglass and carbon fiber, epoxy resin for casting. Epoxy is a sensitizer, which means our bodies do not react to it on the first exposure. Rather, it is on the second or subsequent exposures where we develop what is essentially an allergic reaction. It can even be after decades of using a product before one reacts to it. But reaction can be severe. Here is a chilling but not uncommon description of a reaction:

Open, oozing, and itching insanity hives virtually all over my body and my eyes literally were swollen shut for a week on two separate occasions. Recovery, each time, took better than a month.

Once developed, it is not reversible, and occupational physicians may advise you to not only never use epoxy again, but none of the “two-part” chemicals in that category. No more Smooth-On products, Great Stuff, A-B foam, etc. If you make your living as a props artisan, you pretty much have to do all your molding and casting out of plaster.

It is important to note that permeation data charts tell how long it takes for a chemical to permeate through a glove. This implies that no glove will offer permanent protection; they are called “disposable” for a reason. In fact, the most a glove gets tested is for 6 hours. If you use a pair of gloves all day, don’t set them aside for the next day. In fact, you should throw the gloves away. Trying to stretch the use of a pair of gloves to save money may seem thrifty, but it is actually counter-intuitive. The same is true of any safety measures and products you use. If you use or reuse them improperly, you get the worst of both worlds; you are spending money but not keeping yourself safe. If you feel you are spending to much money on safety equipment to make props, the best solution is to stop making props. You don’t go scuba diving without an air tank. We often get in situations where the easiest solution seems to be to continue on and finish a prop; it’s late and you’ve run out of gloves, and all the hardware stores are closed, and all you need to do is get one more coat of epoxy on so it can cure by the morning and they can use the prop in rehearsal. When you get to those situations, remember this: Your goal in life is not to finish that single prop. Your goal in life is to build props for the rest of your life. Taking shortcuts now will affect your health later on. No prop in the existence of humankind has ever been more important than your health.

A good shop foreman will be consistent in his or her purchasing of disposable gloves, so you don’t have to hunt down the permeation data every time he or she buys a new brand.

In conclusion, don’t get stuff on yourself. You should know what is present in any material or substance you are working with. If it includes chemicals that can be absorbed through your skin, you need to find out what glove will offer protection from that chemical, and how long it will offer that protection. Remember that gloves from different companies may differ in their permeation data, even if all the stats on the box seem the same.