Thursday, 8 March 2012
Curing Fabric Prints
Since a few people have asked me recently about curing prints on fabric, I thought I'd put what I know down here, in case anyone else wants to know.
First off: 'curing' prints means making them permanent, so that the fabric can be washed. If prints aren't properly cured, they'll eventually wash out. (Unless of course you spill ink on your best skirt by accident - accidental ink never washes out, I don't know why.) Uncured prints will feel slimy after a short soak in water; that's the ink coming off.
The ink I use is water-based fabric ink/paint, also called silkscreen textile ink, to be used on plant fibre textiles, and it's cured by heat. Most manufacturers will put some sort of instructions on the container, and usually on their website too, so that's the best place to look for advice. But sometimes this info can be a bit sketchy.
Choose the fabric you'll use carefully. Synthetics are unpredictable at the high temperatures needed for curing; cotton, linen, hemp, or blends of these, are best.
Wash and dry the fabric before printing. It's possible to buy fabric that's prepared for print (PFP), but be wary. I've personally met whole bolts of fabric that swore they were print-ready, but turned out to be lying through their rotten little cotton teeth. Fabric straight from the shop often has sizing in it, which makes the fibres look smooth. When you print on it, you print on the sizing; when you wash the fabric, the sizing washes out, and with it the print. If you're at all unsure, test a small scrap of the fabric by rubbing ink onto it, curing it, and then washing.
The very simplest and surest way to cure prints is to find a local silkscreen company and pay them to do it for you, but that might not be practical.
Curing at home requires an iron or an oven, and a clock. Pretty simple, though not much fun in summer.
What you'll be doing is evaporating all the water in the ink, so that it can bond to the fabric. So the first point is to be sure that the print is quite dry. Overnight drying is a good idea, 2 or 3 days even better. Hang the prints up to dry, if possible; stacks of prints won't dry equally all the way through.
Curing by ironing is as simple (and as tedious) as it sounds. Set the iron to the highest setting, and start. Iron the print from the wrong side - I say this because that's what the websites say, not because that's what I always do - going over and over the printed part. You'll be stopping just short of scorching the fabric; touch it lightly with your fingers, and it should almost burn you. You should also see steam coming off the print. Most manufacturers recommend ironing prints for 3 to 6 minutes; audiobooks and Kindles come in really handy here.
For larger pieces of fabric, oven curing is easier. Set the oven to 180C, and let it heat up. Fold the fabric if necessary, wrap it in a sheet of tin foil, shiny side out, and pop it in the oven. Turn the oven off, and leave it for at least 15 minutes. When you take it out, open up the fabric and shake it out so that the steam can evaporate.
Very large pieces of fabric will need a few cures to ensure that the whole surface has heated up properly. In that case, don't turn the oven off, but keep a careful eye on the clock. 15 minutes should be fine, 10 minutes if you're nervous about the fabric burning. Take it out, shake it, fold it again so that the parts that were in the middle of the bundle are on the outside, wrap it in the foil, and cure again. Do this as many times as you feel safe to do.
Popping the bundle on a baking tray will make things easier, and wrapping the foil shiny side out is a good idea. (This is one of those things that I've been assured is a myth, but the one time I wrapped something shiny side in, the fabric ended up with scorch marks along all the folds, so I keep doing what I do.) Don't forget to use oven gloves.
One more thing: cold cure medium. This can be added to ink so that it will cure by itself, over time. This is what I use, but, ever the pessimist, I tested a few swatches and wasn't entirely happy with the result. So now I add cold-cure to my ink, and heat-cure with an Elnapress iron for 10 seconds. The combination works well (and yes, I'm very glad I got a Kindle for Xmas).
There are many, many things that can affect how well fabric cures, which is why ink manufacturers can seem cagey with their instructions. Even fabric that feels bone dry can have moisture in the fibres, which is why thinner fabrics will cure more easily than thick ones. Environmental humidity can affect things. Ink that's too old might not bond well. It's a bit like baking, really.
But you can develop a feel for it, and if you overcompensate a little, cure things for a little longer than seems really necessary, it should work out fine. If you're unsure of ink, fabric, or curing times, do a test swatch.
Anything I've forgotten?