In silkscreen printing you need to have a solid black image on your film positive to properly expose your stencil with photographic emulsion. If your image requires solid blocks of colour and no gradients or shading then it’s no problem. But if your image is more photographic or has significant gradients and varying tone then you have a problem. When you turn your image to black and white for your film positive you will have significant amounts of grey image area which will not properly expose. So, the best way to screen print photo style images is to use a halftone pattern.
A halftone pattern is a series of dots that vary in size and shape and spacing to create an optical illusion of varying tones and gradients. The dots are so small that the human eye blends them together so they appear as smooth tones.
Creating your halftone image will require some digital manipulation. Adobe photoshop has a number of filters to reproduce your image in a haltone pattern that you can use for your film positive. (filters<pixelate<color halftone, filters<sketch<halftone pattern, mode<grayscale<bitmap). I have had great success using photoshop for producing halftone images. Here’s a more detailed tutorial about using photoshop for your halftone printing.
Or you can use Ben-Day Dots, which are sheets of dots comic book illustrators used to create secondary colors and shading that would combine two (or more) different small, coloured dots to create a third colour. They would be purchased in sheets of transfers and then applied to the needed areas.
My best advice for printing halftones is to experiment first with the size of the dots you will be able to print. But the general rule of thumb for determining correct mesh count to use is 3.5 x halftone line count to get the minimum mesh count. For example, a 65-line halftone image would require a 230-thread/in. mesh or higher. The higher the mesh count, the better the reproduction of the image on the stencil and the print and the less chance of moiré patterns. Avoid any directly divisible mesh/halftone combinations (e.g., 75 line halftone screen on a 300-thread/in. mesh) as this will also cause interference patterns on the stencil and the print. Also keep in mind that yellow mesh is often recommended for high resolution printing with halftones.
Halftone screens up to 32 lines/in. 110
Halftone screens up to 70 lines/in. 305–380
Halftone screens from 70-133 lines/in. 380 –420
Happy Printing!
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{ 14 comments… read them below or add one }
the last sentences tell how many lines is needed and the number after that is the mesh?
Yes, that’s what it is. And I generally find that if I’m doing halftones with 110- I find that a good number for making very noticeable chunky dots is about 17- 19 lines per inch.
I know this is an old post, but I was wondering if this tutorial assumes your using a 300 dpi image? I notice applying a halftone in photoshop, the dots are different based on the dpi of the image…
Thanks
The dpi actually has to correspond to the output of your printer. Mine is a 300dpi printer and so all my images are made for that.
What would the difference be if we are using a white mesh? Does that effect how the image will turn out?
I think that the colours can absorb light differently. I have never used anything but white so I can’t really speak to their differences.
Screen printers generally use dyed mesh (usually yellow) when printing halftones. The reason is that with white mesh, the light from your exposure unit tends to bounce around kind of like light traveling through fiber optic cable. This can fill in some halftone dots. The yellow mesh does not have this problem, but it takes longer to properly expose a dyed screen as a result. I’ve used both and have had good results with both, but most pros use dyed… Whenever I need to order more screens for halftone I go with the yellow mesh just to be safe…
You probably do most of your printing onto paper right? The reason I have almost never used colored mesh is because I only print onto fabric and you need a 110 mesh to get enough ink through onto the fabric for absorption and a 110 mesh is not great for fine halftones- like they use in signs etc. Thanks for the clarification for my readers and for me!
Actually no, I do all my printing on fabric. Namely t-shirts. With higher mesh counts you simply have to use more pressure on your print strokes. Or sometimes multiple strokes. I find it actually gives me a bit more control over how much ink makes it onto the shirt and the chances of you putting down too much ink and having the ink smudge is greatly reduced. I use water based inks which are meant to penetrate the shirt fibers, so when printing I use a firm pressure on the stroke and it usually takes 2-3 strokes to get the desired result. But only the first stroke need penetrate the shirt fibers, each pass after that will bond to the ink in the shirt. if you have some sitting on top, thats okay as lond as it looks smooth. I’ve been printing halftones at 55lpi 25degree angle and on a 230 mesh screen and the result is nearly photo realistic. Its so nice to be able to print whatever I want now… you should try it sometime. I was amazed that it actually worked the first time I did it…
Is the platen that you use hard? Generally t-shirt printers use a hard surface platen (on a press) as opposed to the felt or foam tables yardage printers use.
I must admit I don’t know too much about t-shirt printing but I’d like to try it.
Yeah, I have a homemade press, with a melamine platen on it that I bought for like $15 on ebay. But to be honest with you I would use a hard board no matter what you are screen printing, it will save you a lot of headaches. You could even just use a piece of plywood or something… But the hard surface is going to support the piece of fabric and make the printing a lot easier… They sell melamine sheets at home depot for not too much money. Melamine is particle board with white laminate on both sides to give you a nice flat surface. But if want to try it out sometime get yourself a large flat board and lay your piece of fabric on it with a little spray adhesive underneath. Then take your screen and tape a quarter down flat to each corner of the frame. This will give you a little space between the screen mesh and the fabric. This is called “off contact”. Then just put place your screen on the board and line up where you want to make your print, hold the top edge of the screen to keep it in place and pull your squeegee!!! Give it a shot sometime!
I have printed off-contact on my felt table before if I’m printing paper or plastic but with fabric yardage you always print on contact. But it’s good for t-shirt printers to have a press- it’s so efficient.
You must be using waterbased or acrylic inks or maybe some other textile medium. When printing t-shirts, you alway have off-contact to ensure that the screen mesh snaps back and leaves a nice even texture to the ink. A few water-based t-shirt printers use no off-contact, but I guess it really matters what type of ink you use. The most popular type of ink in the t-shit industry is plastisol and you must have off-contact for it to work properly. with that type of ink, you are actually laying the ink on top of the fabric rather than penetrating it. I use waterbased because it is more environmentally friendly. Really the difference is that some types of inks are meant to be pushed into the fibers of the fabric, others are not… By the way if you don’t mind me asking, what type of ink do you use?
You are sort of right about plastisol inkssitting on the surface of the fabric but the reason that you print off contact is still the hard surface. If you didn’t, whether you used a solvent ink, a water based or acrylic it would smudge printing on-contact. The bounce back of the screen allows the ink to stay in place without the mesh squishing it underneath. I have printed with plastisol inks before on my felt table on contact and they work fine. If tried the same thing printing onto paper or plastic, or on a hard surface I would need to do it off-contact.