Opaque water based inks
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Have you ever painted a wall ? Printing onto dark fabric with an opaque water based ink is similar. When you paint a dark coloured wall with white paint and it looks pretty white, the paint dries and you see the original colour showing through after the first layer dries. Another coat of paint and the wall is super white, the background can no longer be seen. When screen printing, your first layer of opaque water based ink onto dark fabric looks pretty opaque but as it dries you see the fabric colour coming through - you need to dry the ink with a hair dryer, heat gun or even flash dryer. Once the initial layer of ink/print is dry you print a second layer of ink exactly in the same place. Which with the right mesh count and ink you should get a good opaque print.
First Layer
Second Layer
Some people like the effect that a single print gives, a more vintage well worn look.
You need to be able to do two things to get a good opaque print :
1. Keep your material from moving.
2. Line up or register your screen for a second print in exactly the same place.
Table Adhesive - stop that fabric moving
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You get a great water based table adhesive which is an adhesive which gets spread onto your printing board. Once it dries the adhesive is "tacky" which means if you put your hand onto it, it sticks to your hand but you can take your hand away without any adhesive coming off. This allows you to keep your fabric that is being printed completely still. Fabric being printed will stick to the screen when you try lift it if there is nothing to keep it stuck down. It is fine to not use table adhesive if you are printing onto light colours - but it's always nice to be able to put your screen down and print another layer of ink if you haven't cleared the mesh properly on your first print stroke and when you lift the screen you see a little bit of your design not printed properly. You only need a single print to get a good dark, strong clean print onto light fabric but for opaque inks you definitely will need table adhesive. When printing onto dark fabrics you need the fabric to not move at all so that you can register/line up the print for a second layer. If your fabric moves even slightly you won't get a registered print.
A 100ml of Table Adhesive will last you a long time especially if you are a hobbyist printer. When printing corporate jobs and printing a lot everyday I would only use a kilogram tub in a year. A less environmentally friendly method is to use a spray adhesive - it seems like a bad idea for the environment and for your lungs, spraying adhesive and then having it floating into the air for you to breath in - it also settles on things if you spray in the same place making a mess. I would avoid spray adhesive aerosols as they do not stay as tacky and you have to keep reapplying the adhesive quite regularly.
Table adhesive takes loose fibres from each piece of fabric and after a number of prints will get less sticky, when this happens you simply take a wet cloth and wipe the board which will soften and loosen the threads. You then wipe the board dry which cleans away the loose threads, you can speed drying with a trusty hair dryer and it will be as sticky as when you first put it on. Eventually though you would need to reapply the table adhesive. When you reapply the table adhesive make sure to clean away any fabric threads that have stuck to the board as they can affect your print (think princess and the pea) so keep it clean and smooth. I would use a paint scraper and gently remove anything bumpy sticking to the adhesive between wiping
and drying.
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Registering your print
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Hinge Clamps - these you screw into your printing board and the hinges clamp onto your screen. You lift the screen, dry the print underneath and when you move the screen back down the hinges ensure that your screen is in the exact same position as before. Hinge clamps work well for single colour prints but if you want to print more colours you have to make some kind of jig or set something up like a corner made from wood to set your screens into to get them into the same place. Another method is to use a carousel which has arms for each screen to be attached to and you move them around and bring them down over your print in the exact same position each time.
Metal bar with movable stoppers to use for registration of screens
You can with bigger screens make jigs that your screen fits against so that you put the screen in the same place each time. I had my boards at an angle with a metal bar at the bottom. On this bar there was a stopper that the screen fitted against. When I put my screen onto the bar and moved it to the side it would be in the same position as the previous print. There are cheap printing one colour presses which are good to start out on. These will make printing and getting consistent results much easier.
Discharge Inks (Decolourants)
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To get bright colours on dark fabric you can use Discharge Inks which basically work by knocking the dye out of your material and leaving it the original colour of the fabric before it was dyed. You can get discharges that leave the fabric white instead of the natural colour and you can also mix the decolourant into clear water based inks to get the fabric left as a colour. The result is a print that you cannot feel as it is in the fabric, not on top of the fabric. Jacquard have a pretty eco friendly decolourant, you can get ones with formaldehyde in them so look at the ingredients. Once you print your design you take a heatgun and heat the print up which activates the discharge and the design starts to appear. Be careful and do wash tests as discharges only work on 100% cotton fabric and you can't simply mix them with any ink, for example glow in the dark ink doesn't react well with discharges. For Glow in the dark ink, first disharge and then print the glow in the dark ink.
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Discharge ink on screen
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Discharge printed but not heated yet - just looks wet.
Discharge ink being activated using a heatgun.