Ryonet | #PoweringThePrint
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:
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).
This kind of emulsion is highly sensitive, exposes quicker, has a longer self-life and, captures fine detail beautifully. The downside of this kind is that it is VERY sensitive. In fact, it is so sensitive that daylight on a cloudy day would start to expose your image. If you wash the screens out outside, the emulsion would overexpose even the stencil.
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 are a beginner, I would hold off on using this type of emulsion for a while. For this kind of emulsion, you will want an exposure unit with a timer and a darkroom equipped with washout booth and supplies. This kind is great to work into, but you may run into more issues if you get into this type too soon.
Photo by Phound Creative Lab.
Diazo (mixed) emulsion requires the addition of a Diazo powder before printing. This must be mixed into the the entire base prior to opening and printing for the first time, and is often referred to as “sensitizing” the emulsion. When you mix the diazo, make sure to use water with a neutral pH balance like distilled water. You don't want to use tap water because the minerals within the water make interfere with the diazo.
Once mixed, the emulsion may last for two months if you store it in the fridge. 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 six weeks. If the shop is in the mid-80s, the emulsion could last 2-5 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 UV light successfully (most of the time) without any issue, allowing you to wash out this emulsion outside. 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.
Beginners, use diazo. Since it takes 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.
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.
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 X-Vactor, FX, or LFX exposure units can handle both. A printer with the new RXP 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.
The type of ink you're using does affect which kind of emulsion you'll need. For presensitized emulsions, only some of them works for all inks. Depending on the ink you're using, you'll need to look for an emulsion that's either water-based, discharge, or solvent resistant. Plastisol ink can work with all the emulsions Ryonet offers.
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.
If you're working in a spare bedroom, bathroom, garage, or a space where there's a good chance light may enter at some point of the process, you'll want to stick with the diazo mixed emulsions. It's also a good idea to use diazo emulsions if you're using a bulb or an exposure unit without a lid since diazo slows down the reaction of curing.
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.