Tim Bongard

Detailed Models

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So the overall process, start-to-finish is three basic phases regardless of which process (wet or dry) you decide to use. First, you determine the parts you want to make for your project you create an image of those parts. Second, you transfer the image to a type of “photo-resist” material which is applied to a sheet of nickel-silver, brass, or copper. Third, the prepared metal is then soaked in a type of acid called an “enchant” which eats away anything not protected by the photo-resist. The end result is a set of metal parts that look just like the artwork you created.

Overview

Two Basic Approaches

Photo-etching for Model Builders

When I began the quest to teach myself how to do this, I searched the Internet for as much information as I could find. A lot of it is dedicated to making your own circuit boards, which is helpful, but takes you only so far for our model building applications. Other articles that focus on making parts can give you some insights too, but much of that makes you wonder just how lucid the author actually was he or she wrote the piece. I found one article that included car batteries and acid baths and decided take a pass on that advice since it contained several creative ways to fry myself or burn my house down with a distinct possibility of managing both simultaneously. Safety precautions aside, the reasonable articles basically underscored that there are two practical approaches to doing photo-etch. One process uses a photo-resist material that is applied to the metal sheets using water, and uses a negative image (parts in white on a black background) that is exposed onto the resist using bright sunlight or a UV light source. This is the classic, traditional photographic approach, and we’ll call this process a Wet / Negative process. The other route is more direct and uses a laser printer or copier to imprint a positive image (parts in black on a white or clear background) directly onto the photo-resist material. This method we’ll call a Dry / Positive process.

Here is a start-to-finish layout of the steps you need to create photo-etch parts:

Of all the various modeling techniques I’ve tried to master over the years, making photo-etch parts is probably the most complicated. Not that it’s difficult – it isn’t – it just involves a lot of steps, and these steps can require special precautions or have to be done under certain conditions. Still, when it comes to finding a way to create certain parts, the photo-etching process is really hard to beat. So what I decided to do was document the process from start to finish and see if there are ways to makes this a little more accessible to our members if anyone wants to give this a go.

What makes the overall photo-etching process so complex is that getting from concept to finished parts actually takes three separate processes; 1) preparing the artwork, 2) preparing the metal and, 3) etching the metal into finished parts. Once you start to break the process into these separate operations, it gets a bit easier to follow and understand, so let’s start by getting a birds-eye view of the entire process and then we’ll discuss each of the steps in turn so we can start making parts.

Photo-etching is a process where metal plates – usually nickel-silver, copper, or brass – are dipped in an acid bath which eats away metal to form detailed parts. An image of the part desired is fused to a piece of metal using a material called “Photo-resist” which is resistant to the effects of the acid. When you pull the metal sheets from the acid bath, all of the unwanted metal material will be eaten away leaving behind a detailed part. Depending on how the resist is applied to the metal, you can actually get pretty fancy and essentially etch the metal twice – first to get the basic part, and then to etch details into the part you are creating. This is what gives some photo-etch parts extra details such as rivet marks, screw or bolt heads, lettering, panel lines, or the like. Nowadays when you buy an aftermarket sheet of detailed parts they can be exceptionally detailed, but getting to that point takes practice and mastering all three steps in the process. Fortunately, most of the parts you may need on the front end will be fairly easy to make and then getting into more complicated etchings is a matter of practice and adding to your bag of tricks. And while it seems like a really a pretty involved way to get parts (which it is…), I’ve never done anything in the hobby that has given me the satisfaction or sense of accomplishment the way photo-etching does. When the finished parts come out ready to add to your model, it really makes you feel like you have accomplished something unique!

Wet Vs. Dry

AN OVERVIEW OF PHOTO-ETCH PROCESSES AND THE STEPS INVOLVED IN CREATING FINE DETAILED METAL PARTS...

Please ask for permission before reproducing, copying, or publishing. Contact the author at the email address above.

From the chart above, a quick look will tell you that the positive / dry process has fewer steps than the negative / wet process. Most of the steps skipped in the positive / dry process have to do with preparing the metal with a light sensitive material. The positive / dry process generally uses some kind of xerographic process where a carbon-based toner is ultimately used as a fusing agent to bond to an acid resistant material (seen to the right), which in turn is bonded to the metal you chose to use.

On the other hand, the negative / wet process uses a more traditional photographic approach where light sensitive, acid resistant material is bonded to metal sheets, usually using water much in the same way that a decal is bonded to a model. The image of the items to be created is transferred to the light sensitive medium using a film negative. UV light from either the sun or an ultraviolet light source hardens the medium in places where the light passes through the negative. After the plate has been exposed to UV light, the unexposed, soft parts of the medium are dissolved off the plate using a “developer” solution (as seen in the photo to the left). Now devoid of the protection afforded by hardened photo-resist material, this allows those unwanted areas of metal to be etched away when soaked in acid.

The critical difference between the two processes is that it is far easier and quicker to transfer the artwork to the metal using the dry / positive process. The water transfer of the photo-resist in the wet / negative process is not only harder, but has to be done in subdued light conditions, preferably under a safelight or low-watt yellow or orange bulb. Even with a ton of traditional darkroom experience, I found this wet / negative process long, drawn out, and tedious. The dry / positive process was as easy as printing out the artwork on resist material and fusing the resist medium to the metal using a laminator. I could do it in broad daylight and have a sheet ready to etch in a few minutes compared to an hour or more including the time needed to set up all the equipment or make sure I had somewhere relatively dark to work.

Where the wet / negative process excels is when you want to etch a piece from both sides. You do this either to cut through heavier stock faster, prevent undercut, or when you want to etch some form of relief into the piece such as an artistic seal or logo where only a portion of the metal is removed. Aligning transparent negatives is a little easier than registering the dry / positive material on two sides of a sheet of metal. There are, however, ways around that which I’ll discuss later in this series.

So what did I do? Which did I choose? Both actually. Micro-Mark has a neat little kit that is reasonably priced and will give you just about everything you need to get you started using the wet / negative process (at right). You get a tank, air pump, and everything you need to start. They supply you with negative material that you use to print the negative in an ink-jet printer. They also supply you with the light-sensitive resist that is applied to the metal. They fully support the kit by having additional supplies and materials available, so once you get the hang of things you can keep yourself supplied with what you need.

With the basics in hand, I then bought a supply of a photo-resist product called “Press N’ Peel Blue” which you run through a laser printer (at left) in order to do the dry / positive process. As time went on I expanded my etching tools to include a larger Pyrex pan and airstone so I could etch larger sheets, and other items to make the process safer and expand my capabilities, but having both processes available for use is by far the best approach.

In the next installment I’ll dive into the steps in more detail and walk you through how to create your own set of parts. In the meantime, if you have any specific questions about this, feel free to send me an e-mail at himself@oldimagineer.info and I’ll reply and be sure to cover that in the next installment as well.