Several types of emulsions exist on the market. How do you decide on which emulsion is best for you? First, you must ask yourself a few questions:
- What experience level do I have with screen printing? Am I a beginner, intermediate or pro?
- What type of exposure unit do I have?
- What environment will I be washing out my emulsion in? Is it light-safe
- What kind of ink will I be using?
Asking yourself these kinds of questions will help you save time and money in the long run. Once you have these answers, you can look at the pros and cons of each kind of emulsion and compare them to your resources and experience. There are two main categories of emulsion: Presensitized or Diazo (mixed).
PRESENSITIZED
This kind of emulsion is highly light sensitive, exposes very quickly, has a long shelf-life and captures fine detail beautifully. The downside of Pre Sensitized Emulsion is that it is VERY sensitive to UV light. In fact, it is so sensitive that daylight on a cloudy day would expose your image. If you wash your freshly exposed screens out outside, your image area will be exposed and you will be unable to rinse out anything.
When exposing a screen, you have a 10% window of error. For example, say you expose a screen for 60 seconds. The 10% window of error would mean you could go six seconds over or six seconds under before you'd start seeing issues with your exposed emulsion. If the screen is under-exposed, parts of the image will wash out. If the screen is over-exposed, you won't be able to wash out some of the finer details of the stencil.
If you are a beginner, I would hold off on using this type of emulsion for a while. For this kind of emulsion, you will want a light safe dark room, an exposure unit with a timer and a darkroom equipped with a washout booth where you can rinse out your image in a light safe environment. Pre Sensitized Emulsion is great to work into, but only after you have built out the ideal dark room
PROS:
- Exposes faster.
- Longer shelf life (up to one year).
- Great detail resolution.
CONS:
- Very sensitive — not for units without timers and needs to be washed out in light safe area.
- If slightly over or under exposed, you will have washout issues (remember the 10% window of error).
- More expensive compared to diazo-mixed emulsions.
A good example of presensitized emulsions are Baselayr Complete, Baselayr Plastisol, Chromaline ChromaBlue or Chromaline ChromaLime.
Photo by Golden Press Studio
DIAZO (MIXED)
Diazo (mixed) emulsion requires the addition of a Diazo powder before printing. This must be mixed into the Emulsion prior to coating a screen, and is often referred to as “sensitizing” the emulsion. When you mix the diazo, make sure to use distilled water. You don't want to use tap water because the minerals within the water interfere with the diazo. Also, use a wooden stir stick, like a popsicle stick or a paint stir stick to stir in the Diazo. Do not use metal tools as these can add minerals into the emulsion which can cause it to go bad.
Once mixed, the emulsion can last for up to 8 weeks if you store it in the fridge at around 40-50°. Do not store it in an environment that's too cold because the emulsion can freeze. If you store the diazo emulsion on a shelf in your shop that's in the mid-70s, it could last for up to six weeks. If the shop is in the mid-80s, the emulsion could last 2-3 weeks. Above 90° you are looking at a shelf life of about 1 week, maybe as long as 2 weeks.
The diazo-mixed emulsion takes longer to expose but is more forgiving. The 10% window of error also applies to diazo-mixed emulsions. Since it takes longer to expose diazo emulsions, your window of error is larger. Say you expose a screen for 10 minutes; you could go over or under by a minute.
Diazo emulsion works great with units that do not have timers and it can be washed out under indirect UV light (meaning fluorescent tubes on the ceiling) with careful attention. If you need to rinse out your image in a UV intensive area, or outside, please spray your screen, get the image area very wet, then place it in a dark trash bag before heading outside to spray out your image. Diazo-mixed emulsions are also cheaper and less of a headache for those just getting into screen printing. This type is more forgiving, while still retaining high quality and detail.
PROS:
- Cheaper.
- Forgiving on under or over exposure.
- Can be washed out under UV light (as long as you have made the stencil wet before bringing the screen outside: sunlight can still expose the image).
- Offers good detail.
- User-friendly.
CONS:
- Shorter life span.
- Must mix to use.
A great example of diazo-mixed emulsions are Baselayr Long Lasting and Chromaline CP-Tex Emulsion.
EXPERIENCE LEVEL
Beginners tend to use diazo emulsions. Since they longer to expose, it's more forgiving to errors whether it's from exposing issues or light leakage. Remember the 10% rule, if it takes 10 minutes to expose a screen, you could expose a minute over or a minute under before you start running into issues.
LEARN HOW TO MAKE A BETTER SCREEN
Intermediate printers, it'll depend on your space and how comfortable you are with your skills. If you have a solid exposure unit and a light safe environment, you could start dabbling in presensitized emulsions. Keep using diazo emulsions for your jobs and play around with presensitized emulsions.
Advanced printers, use whichever emulsion you want. At this point, you have a solid darkroom and a strong grasp on the craft. Focus on other factors like what ink you're using to decide what type you need to use.
EXPOSURE UNIT
Printers using a UV Exposure Bulb, an X1620 LED Exposure Unit , or an exposure unit without LED bulbs, use diazo-mixed emulsions.
If you have an exposure unit with a lid (especially a vacuum-seal lid) and it has LED bulbs, you could use either diazo or presensitized emulsions. Units like the V2331 LED Exposure Unit, or Y3942 LED Exposure Unit can handle both. A printer with the new X2536 LED Exposure Unit could also use either types of emulsion, depending on how much compression they can get on the lid (the more compression means the better the presensitized will expose). Evaluate how comfortable you are with your skills and how fine of detail you need for your stencil to determine which emulsion will be best.
LEARN ABOUT THE NEW X1620 LED EXPOSURE UNIT
INK
The type of ink you're using does affect which kind of emulsion you'll need. For all emulsions, only some of them work for all screen printing inks. Depending on the ink you're using, you'll need to look for an emulsion that's either High Solids Water Based, discharge, or solvent resistant. Plastisol ink will work with all the emulsions Ryonet offers.
Emulsions for Water-Based and Discharge Ink:
Solvent-Based Ink:
DARKROOM ENVIRONMENT
Is your darkroom light safe? Do you have an exposure unit with a timer and vacuum lid? Is your washout booth in the same room? If you work in a space that doesn't permit any light to enter and you have the right equipment, you can use either presensitized or diazo mixed emulsions.
LEARN ABOUT THE IDEAL GARAGE SETUP
Insider Tip: If you're using your backyard as your washout booth, try wetting your screen with a spray bottle before you go outside. By wetting the screen, you'll help prevent the emulsion from cross-linking with the screen before you're able to wash it out. It's also a good idea to put the screen in a black garbage bag when bringing it outside to further prevent the emulsion from cross-linking.