Photos & notes from trying the mineral oil method of image transfer in screen printing

Materials

Making the screen: mineral oil (baby oil), paper, printer, screen, photo emulsion, paint brush (to apply mineral oil), light table or hanging lights. Optional: fan, bug lights.

Printing: screen printing ink, paper or fabric where you will print, a squeegee. Optional: hinge clamps, hair dryer.

Making the screen

Step 1: Create the design on a computer

I started with hand-drawn artwork, then took a high resolution photo and traced it in Adobe Illustrator to make a scalable digital design.

I used colors as placeholders in Illustrator to help me imagine what it would look like when I printed it. I decided on bright purple paper with two layers of prints. For the background layer, I chose a muted purple color and for teh foreground layer, I chose a bright turquoise ink. The actual inks will end up being a little different, but the colors on the screen help me plan out the layers.

Step 2: Print the design in layers

Print: Even though the design has color, you always print out each layer as a black and white image. This is because you want to have the greatest amount of contrast in your design when you’re burning your screen. So I exported each layer separately and printed them onto regular office paper.

Since I have two layers that will be printed on top of each other, I added registration marks to the design — those are the circular targets the corners. The idea is that on the second print, you can line up the image easier and then print it in exactly the right spot. I also added cut marks outside of the design, those are the two lines that make an “L” shape in each corner. Both the registration marks and cut marks are optional, and as it turned out I didn’t end up using either.

Trim: To save space on the screen and fit both designs on one screen, I trimmed down the white space around the designs. These cuts were very rough, I was just trying to cut down the space we’re using on the screen.

Step 3: Coat your screen in photo emulsion

Coating the screen with photo emulsion is next. It takes time to dry so often I actually do this step much earlier, sometimes even before I begin making the digital design. The goal here is to coat both sides of the screen with a thin, even layer of emulsion. There are a couple challenging parts to this: photo emulsion is light-sensitive and applying a thin coat is tricky.

Seeing in the dark: It’s difficult to properly coat a screen when you’re working in the dark. Photo emulsion is sensitive to light, meaning that you need to keep your coated screen in a dark room until after your expose it. Most household light bulbs will cure the emulsion, so for a long time that’s how I did it; I worked in the dark. Not any more.

To be precise about this, screen printing photo emulsion is sensitive to Ultraviolet (UV) light, a part of the light spectrum that is not visible to humans. UV light is present in most household lights to some extent and, of course, it is also in sunlight. So if you’re working during the day, curtains are a must. Each time of light exposes photo emulsion at a different rate, depending on how much UV light is present. Halogen lights have a lot of UV, incandescent bulbs have a significant amount and even LED lights, florescent lights and compact florescent lights (CFLs) emit some UV light. There are specialty bulbs that you can use for screen printing that will not cure your emulsion, but they are expensive. I’ve only found one type of bulb that is both safe for screen printing and also very cheap and accessible: bug lights (~$5).

These incandescent “bug light” bulbs are intended to be used outside without attracting mosquitos and moths. With a yellow coating on them, they filter out most of the UV light. And they’re bright enough that you can see while you’re coating your screen.

I have one of these bug lights in a clamp-light that I use in an otherwise dark room while working with photo emulsion. Being able to clearly see your screen, makes coating a screen much easier.

Spreading an even coat: An even coat of emulsion is crucial for burning a good screen, especially if your design has fine detail or thin lines. If you have lumps of emulsion on the screen or areas with thicker coats, your screen will need different amounts of time to expose properly — thicker areas require longer exposure, thinner areas need less time to expose. This may result in losing some detail in your design. That’s no good. So you need an even coat, but that’s harder than it sounds.

For years I used a spoon to scoop emulsion onto the screen and then used my squeegee to spread the emulsion from top to bottom. This is probably the most common method for coating a screen among DIY printers because it does not require any specialized tools — you can use the same squeegee that you will later use for printing. I used my printing squeegee for years until I learned about scoop coaters. Now I use a scoop coater every time.

Get a scoop coater: This tool is designed to help you spread an even coat across your screen. I bought mine on ebay for around $40. How does it work? Start by adding a few big spoonfuls of emulsion to the scoop — double or triple the amount of emulsion that you actually need on the screen. Having extra emulsion in your scoop ensures that there is enough flowing while you spread it. You can always save the excess emulsion afterwards by scooping it back into your container.

To start coating the screen, push the scoop up against the bottom of the screen and slowly pull it up towards the top of the screen. As you’re dragging the scoop coater up the screen, it should be pouring thinly and evenly across the mesh. Repeat on both sides of the screen. If it didn’t work the first time, try a second coat while it’s still wet.

Once your have a coated screen, put it in a dark room and let it dry. If the coats are thin, it can dry in as quickly as one hour. If you have a thick layer, it may take a few hours. Put a fan on it to speed up the drying time.

Step 4: Apply the baby oil

After a couple hours, we have a screen that is coated in photo emulsion. It’s dry to the touch, but what you can’t see or feel with your hands is that the emulsion is not cured.

We also have our designs printed out. It’s now time to use the mineral oil and a light source to burn the design onto the screen.

Start by arranging your designs on your screen. The flat side of the of the screen is the “bottom” and this is where it is best to place the designs, but remember to flip them backwards. When you’re printing, you will be printing with the flat side of the screen on the bottom, so make sure that you place your design on there properly.

Now pour a few drops of mineral oil on the paper and spread it evenly across the paper. It will only take a few drops and it will be easier to clean up if you use as little oil as possible, so use the oil sparingly.

Coat the entire sheet with oil. There will probably be some air bubbles under the sheet.

Use the back of the paint brush to gently push out any air bubble. This should be very easy to do, but be careful to not tear the sheet of paper.

Once the entire sheet of paper is translucent and the air bubbles are all out, you’re ready to move on to exposing the screen.

Step 5: Expose the screen

Depending what you have available, you could expose your screen many different ways. The idea here is very simple, you just need a UV light shining on your screen, with the design between the two. Your design will block some light and the rest of the emulsion will cure. For example, you could put the screen on the floor and have an incandescent light hanging above it. Or if you have a halogen flood light, I’d recommend using because the time it will take to expose the screen is much shorter. How long you need to exposure it will depend on your set up. If you’re using QTX emulsion, you can expect your exposure time to be around 15–20 minutes with an incandescent bulb. If you’re Diazo emulsion (speedball’s variety), your exposure time will be more like 45–60 minutes. After experimenting with various exposure times and bulbs, I built a light table so that is what I use now. Although there are many ways you could do this part, I’ll share how I do it.

This light table is huge, it’s 5 feet x 3 feet. I made it from scrap wood and the top is a sheet of glass. It has two halogen work-lights mounted inside on the bottom, facing upwards. The work lights came with glass covers that filter out some UV light to protect your eyes. I removed the filters because the goal is to maximize the amount of UV light hitting the screen.

The two lights are spaced out so their light overlaps in an area of around 4ft x 2ft in the center of the glass. This is the best location for the screen because it gets an even amount of light; Placing the screen further out on the edges will mean it gets light primarily from one of the lights, instead of getting it from both bulbs. I have the lights plugged into a power strip with a switch on it, so when it’s time to turn on the table, I flip the switch on the power strip.

To expose it, I place the screen on the table, face down. Remember: however you are exposing your screen you need to arrangement to have your design between your light source and your screen. This may sound obvious, but it’s a common mistake to put the design on the wrong side of the screen and accidentally expose the entire screen.

Using this light table, exposing a screen only takes 11 minutes. After 11 minutes, I remove the screen and take it to a sink or bathroom to wash it out.

Step 6: Wash out the screen

The screen may not look any different yet but as we wash it out, the image will start to become visible. The goal here to so wash out any emulsion that has not be cured — this is the emulsion that is behind the design.

Take the exposed screen to a bathroom, set up a bug light, remove the paper and blast it with water.

The design should start to become visible within a couple minutes. If the design isn’t coming out right away, slightly scrub the screen with your finger to push out extra emulsion.

You’re done washing out the screen once the design is entirely visible and there is no emulsion left in the places where you intend to print. It’s a good idea to use a little soap while cleaning the screen to get rid of any remaining baby oil. Dish soap is ideal because it removes grease quickly, but bathroom soap works too.

After washing, leave it to dry. You can now keep the screen in the light. In fact, it’s a good idea to intentionally expose the screen for a little longer to make sure the emulsion is fully cured. You can do this by leaving it to dry in a well-lit room or by putting it back under your light source.

Once the screen dries out, you’re ready to move on to printing.

Printing

Now that we have a screen burned, it’s time to make some prints. This particular design has two layers but they don’t require very tight registration. Even though I put registration marks in the design, they didn’t come out well on the screen so I didn’t even use them while printing. I just guessed at the positioning, as you can probably see from the prints. Here are the steps for printing.

Step 1: Tape off the sides

There is a lot of area on the screen that is not covered by emulsion. Without emulsion covering theses spots, ink will go through the screen and print in those areas. The edges are a good example; You can see that there is a wide gap between the edge of the frame and beginning of the pink emulsion. Using masking tape or painter’s tape, fill all the gaps on the screen.

Make sure to cover all the empty spots.

Choose color, choose inks

Remember this is a two layer piece, so we need two colors. I wanted a muted background color and a bright foreground. The paper that I’m printing on is a lilac purple color and I bought a bright turquoise ink for the foreground. Those two colors together will provide high contrast. For the background print, I didn’t have a good purple ink but I did have blue, red and white.

So I mixed colors, trying to get a muted purple.

The resulting color wasn’t ideal, it came out a little too darker than I intended but the contrast between the turquoise and purple will hopefully overpower the dark background. Ok, now it’s time to print.

Set up the press

All you really need to print is the screen and your material, but there are some simple ways that you can make printing a lot easier for yourself. If you’re doing more than one print, like I am, having a way to keep your screen in the same position is helpful for lining up your prints. I use a homemade press to keep things lined up. I didn’t make this press myself, a couple of friends made it from spare parts and I inherited it.

The hinge-clamps are the key part of a press. They are two clamps that are attached to a hinge so the screen can fold up and down but it will not move along any other axis. The hinge clamps that I use are made from two vice grips and two door hinges. You tighten the hinges down on your frame and the hinges are fixed to a piece of wood. So you can fold the screen down when you’re printing and fold it back up when you’re switching materials. You could also buy hinge clamps ($30) that are specially made for this.

So if you’re you’re using hinge-clamps or a press, clamp the screen to your press, put the paper that you want to print on underneath and now we’re ready for the first print. If you’re not using one, just place the screen on your sheet directly.

Pull & fill

A quick note on inks: There are a many different kinds of inks that you could use to screen print. Mostly there are two types that you need to consider: water-based inks and plastisol inks. Unless you have a lot of experience or are printing commercially, use only water-based inks. They’re easier to work with, they’re more common and you can get them in small amounts at most craft and art stores. Plastisol inks don’t dry at room temperature, they need to be heat-cured. Water-based inks can dry at room temperature. Almost all screen printing inks that you would buy at an art supply store are water-based. Everything made by Speedball is water-based. I almost exclusively use water-based inks.

The technique for printing with water-based inks is simple, it requires two pulls. First you fill your screen with ink, then hold your squeegee at a 45 degree angle to the screen and firmly pull ink through the screen and onto your material. Then — and this part is very important — you follow up with a second light pull to fill the screen with ink again. Water-based inks dry very quickly and the purpose of the second pull is to fill the screen with a thicker coat of ink so that the ink does not dry while in the screen and block your mesh. If your ink does dry while printing, you’ll need to clean out your screen and start again. After the two pulls, fold the screen up.

I was working with a large sheet of paper, so I moved the print over and repeated the print multiple times on the same sheet.

Wash out the screen

After doing all the first layer, it’s time to wash out the screen.

Using warm water, scrub the ink off the screen. Allow the screen to dry before printing again.

Printing a second layer

Before printing the second layer, it’s important that the first layer is completely dry. I was impatient, so I used a blow dryer to dry the ink from the first layer.

To print the second layer, just repeat the same process as above, but using the prints from the first run as the base. Lining up your layers can be tricky. The best way to line up layers is to do some test prints on newspaper and then mark on your press where the prints are landing. Then when you’re placing your material down, you can line it up with exactly where the print is landing. For this project, I didn’t care too much about lining up the two layers perfectly, so I just guessed each time. If I were printing a design that required tighter registration, I would definitely line up the layers for each print.

After printing the second layer, it’s starting to looking more and more like the initial design. Now it’s time to clean up and next up is cutting & folding the cards.

Wash out again

For the second time, we’ve got to wash out the ink from the screen. Again, using warm water scrub out the ink. The screen may change color from the ink, which is fine. You just want to make sure that no particulates are left in the screen to clog it up for next time.

Cutting & folding

Now to put the final touches on these cards, I folded them and trimmed them down to size. Here’s a tip: Fold first then cut to make sure your cuts are straight on both sides.

Write and mail them

Nice! Now we’re all done with the cards. Now it’s time to write them and mail them out to friends.

Pros and Cons of the Mineral Oil Technique

In general, I like the mineral oil technique. Printing onto transparencies can be tricky and sometimes expensive. When using transparencies, you need to make sure you buy the right kind for your printer — laser printers, toner photocopiers and ink-jet prints all need different kinds. If you use the wrong kind of transparency, it might melt inside your machine or the ink might rub right off. Being able to print right onto paper makes prepping screens a lot quicker, but the downside is that you don’t have a reusable design; After you coat the paper with oil you need to throw it away. With a transparency, you can hold onto your design and use again to burn another screen another time. Another downside to the mineral oil method is simply that you have oil in your workspace. Oil stains fabric and paper. I accidentally left some mineral oil on my screen and when I was printing, it transferred to some of the cards, leaving greasy spots. I had to throw away a handful of prints because they got covered in oil spots. To avoid this next time I’ll use dish soap or another degreaser to make sure I clean off all the oil before printing.

More Experimenting Ahead

I enjoyed learning this new technique. I’ll be experimenting with mineral oil exposure more in the future. I haven’t found much written about this technique online, so I hopefully this piece helps demystify it. Let me know if you have any experience with this method or if you have any advice to share.