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08

Screen-printing Notes

I often get asked by students and ex-students for a copy of the notes I give out during my screen-printing class so I have decided to put them up here so people can have access to them at all times without having to contact me!

Happy printing! - Bruce Mahalski(Screen-printing Tutor)

 

Screen-printing on Paper and Fabric

You can print just about any design on paper or fabric- from a simple one colour line drawing to a full colour photograph.

 

STENCILS


Stencils are the means by which designs are applied to a screen. They function as physical barriers – blocking some holes on the screen’s mesh and allowing ink to penetrate others.

Stencils can be made from a wide variety of materials including paper, thin cardboard, masking tape, clear film (acetate), masking film and photo-emulsion. Simple paper, card or clear film, stencils can be hand-cut and applied to the back of the screen using masking tape(or made using the tape itself) but masking film and emulsion  stencils are applied using simple chemical processes.

You need to make a new stencil for each separate colour of your design.

Paper and Cardboard Stencils

Brown butcher’s paper is ideal for cutting stencils from but any strong firm paper or thin card is good. The design can be first drawn onto the paper/card and then cut out using scissors or cutting blades before being taped on to the back of the screen.

Paper and card stencils degrade quickly and can usually only be used for one session of printing so they are best for short one-off print runs and experiments. They can also be used to temporarily (or permanently) cover the backs of screens to block off any areas on the design you do want to print or for covering pin-holes in the emulsion outside the design area.

Clear-Film (Acetate) Stencils

Clear film can be bought inexpensively by the sheet in different sizes from any art supply store. The film is placed over the top of a design (or has a design traced onto it) and the correct areas are cut out using a sharp blade. The finished stencil is attached to the back of the screen using tape, Clear film stencils give you nice sharp edge lines and if they are carefully removed(and allowed to dry) they can be used for many subsequent print runs.

 

Hand-cut stencil screen-print  by New Zealand artist Debra Bustin - 1980's.

 

Photographic Emulsion Stencils

Firstly make your stencil by applying your artwork/design to a sheet of clear film or tracing paper. The aim is to achieve as dark an image as possible because this physical layer protects the light-sensitive emulsion underneath and prevents them from hardening. This soft emulsion can then be washed out of the screen leaving the design area as a negative space which ink can be forced to create the positive design. Your design should be at least 10 centimetres smaller(all around) than the interior of the screen you are going to use so you have enough space for your ink and run-off.

 There are a number of ways to get the design on the transparent sheet.

1)      It can be simply drawn onto the film or tracing paper using an indelible red pen (There is a special pen called a Rego-Redline pen for doing this but any indelible pen will do). You may need to go over both sides of the image to get a really dark ‘light-proof’ line.

2)      You can photocopy or ink-jet the design onto the tracing paper or film using a photo-copier or home printer. Hold the finished copy up to the light and see how dark it is. You may need to go over any faint areas on the back with one of the pens above. To make the design darker you can also lay two copies of it over each other.  

 

  A design photocopied onto tracing paper (right) and then exposed onto the emulsion of  a screen.

3)  Usually the best (i.e. darkest) results are achieved by machines at professional copy houses which put down a thicker layer of ink that home printers or photo-copiers. Just about any copy house will print out an A3 ‘transparency’ for $5 or less. 

APPLYING THE STENCIL TO THE SCREEN

Once you have a finished stencil you can prepare your screen.

1) Degrease both sides of the screen using jiff or any other cream cleanser; rinse it with cold water and leave to dry completely. This process removes any dust or grease from the screen which may cause small holes in the emulsion (‘pin-holes’) or make it impossible to remove later on.

2) Get some light-sensitive emulsion (Make sure the dry powder activation chemical has been added!). The emulsion should be kept cool and not left in a warm room overnight (therefore I keep it in the bottom of the fridge). Once the activation chemical has been mixed in it lasts for about six months but in its inactive state it stays good indefinitely. It costs about $65 for a litre of emulsion which is enough to coat about 25 standard size screens.

3) Pour emulsion into a coating trough or onto a squeegee and coat the screen carefully with an even layer on both sides. Scrape off any excess with a spatula or piece of card and remove any emulsion from the frame.

4) The emulsion is not light-sensitive when it is wet but becomes so once it is dry so the coated screen should be allowed to dry in a warm dark room. A fan heater should be used to accelerate this process otherwise it may take all day (or longer!). If you are drying a number of screens at once put blocks of wood between them to allow the air to circulate freely. When you remove the screens be careful that no bits of wood are sticking to the backs of the frames (as they can come loose and fall through the mesh of the screens below!).

5) When a screen is completely dry it is ready to expose. You can store it in a dark room (or under blankets) for up to six months before you use it so long as no light gets onto it.

Exposing Screens

1) It is possible to expose a screen using day-light alone but this may take all day. A bright light of any sort is best. We use 750 Watt Mercury Vapour lamps which produce a very bright light and expose the screen very quickly. The light can be above, below or beside the screen so long as it is exposing the surface which is covered by the stencil. When you buy the emulsion you get a chart giving details of recommended lights, exposure times and the distances which you should place your coated screens from the lights. At the art-school we have the light 70cm above the screens and expose them for 8 minutes.

2) We lay the transparency back to front on the back of the screen with the light above it. If you look at the screen from the front the design should be the right way round.

3) Put a sheet of glass or Perspex over the stencil to keep it flat.

4) Expose the screen for the correct amount of time. It is best to turn on the light a few minutes beforehand to make sure it is at its brightest.

5) Remove the screen and your transparency. Put the transparency somewhere safe. You will need it later to help you register your prints.

6) Quickly cover both surfaces of the screen with cold water to stop the exposure process. Use the water stream to wash the soft emulsion out of the areas covered by the stencil until your design area is completely clear. When you have finished hold the screen up to the light and check all of your design area is completely free of emulsion.

7) Dry the screen with a fan heater until it is completely dry. Tape up the edges of the screen to block any areas not covered with emulsion. Check for pin-holes. These are small holes in the emulsion area caused by dirt on the glass, marks on your transparency or solid matter in the emulsion. These can covered using tape on the back of the screen or painted over using with emulsion before re-exposing the screen.

 

A freshly exposed screen after the soft emulsion has been removed from the design area with a water-blaster(Note - the clear print area is  white  and the remaining emulsion is blue.)

 

Stencil Removal

When you have finished with a design you can remove it from the screen using Screen-Strip. This chemical comes in the form of a dry powder.

1) Mix about one table-spoon of the powder with one litre of hot water.

2) Coat both sides of the screen with the solution – leave it for a few minutes – and then blast it off using a hose (or preferably a water-blaster)until the screen’s mesh is completely free of emulsion.( Make sure the dirty water goes down a proper drain and not directly into the storm water system!)  You will still be able to see staining on the mesh where you have printed your previous designs but this will not affect your next exposure.

3) You can then re-jiff the screen and then when it is dry re-coat it with emulsion and expose another design.

(Note - The longer the image has been on the screen the harder it is to remove. If it  has been or the screen for a year or more you may need to re-coat the screen with screen-strip and then water blast it again to remove it completely. Or else you may never get it off and will need to put new mesh on your frame.)

INKS

There is a large range of different inks for printing different surfaces and obtaining different effects. You don’t always need to use ink – often paint can be just as good. You can print with almost any liquid at all but you may have trouble removing some liquids from the screen once you have finished. At Inverlochy we try and stick to water-based inks which are easier to clean up than oil-based inks and less damaging for the environment (we hope!).

 

 

Rolling on an undercoat of standard fabric inks

 

STANDARD FABRIC INKS (FOR FABRIC ONLY)

 

These water-based inks are suitable for printing any fabric with a cotton base (i.e. containing 60% or more cotton.) You can print drills, lawns poplins, canvas, linen, knits and cotton lycras.

The finished colours are made up of a combination of pigment (which is usually bought in small 100gm bottles) and a colour-less base (bought by the litre).  To make up a colour mix roughly a table-spoon of pigment with a litre of base.

The pigments cost between $5-20 for 100gsm and the base costs $5 per litre. Standard inks are by far the cheapest with a mixed litre(pigment and base) costing around $7.

These inks work by sinking into the fabric and dying it. They can not be printed over the top of super-opaque inks as they will not sink in and will wash off later.

They can be used for any light-coloured fabrics but will not be visible when printed onto darker fabrics. They are the most liquid of the inks we use and the easiest to print with.

Before a print can be washed it needs to be heat-set. This is done by placing the finished fabric or garment into a dryer and spinning it on the hottest setting for 15-20 minutes until the fabric is too hot to touch comfortably. It can also be ironed with an iron on its hottest setting (Usually ‘Linen’ or ‘Cotton’) until once again the whole surface of the print is too hot to touch comfortably. Over a period of months the ink will naturally set itself even if it hasn’t been properly heat-set.

Once set the print should only be washed in cold (or occasionally warm but never hot) water and should last as long as the fabric does.

There is a chemical called ‘Cold Cure’ which can be added to the ink which means it does not need to be heat-set but it is a nasty substance that needs to be used with thick gloves and lots of ventilation.

 

SUPER-OPAQUE(OR SUPER-COVER) AND METALLIC  INKS (FOR PRINTING FABRIC AND PAPER)

 

These water-based inks work by laying down a reflective layer on top of the fabric/paper rather than sinking in and dying it. They are usually used for printing dark coloured fabrics (e.g. black/navy/brown) where a standard ink would be invisible but can also be used to print thick papers, cards and even wood to good effect.

 They are much thicker (like whipped cream) than the standard inks and more difficult to print with – firstly because you have to lay down a thick layer of the ink which often necessitates two/three coats – and secondly because you can’t see through the screen to register once you have done the first print. They always need to well stirred before use.

You can buy super-cover base and mix in standard pigments to create colours but I would recommend that beginners buy them ready mixed by the litre as they can be difficult to mix well(particularly white and the metallic inks). As with the standard inks they are fixed by heat-setting or adding cold-cure (which also enhances their elasticity). Printed garments should be washed in cold water. Because these inks sit on top of the fabric they can be rubbed off by friction so it is a good idea to turn the garment inside out when washing or tumble drying which keeps the print looking strong and sharp.

They can be thinned using small amounts of water or super-cover base or by adding ink softener.  Lighter colour tones can be made by mixing super-cover inks with standard inks or by adding pigment to pre-mixed white super-cover.

These thick inks air-dry quickly and therefore need to be printed quickly. If you leave the screens too long between prints they may become permanently clogged with dried ink. 

They are quite expensive costing between $38-55 per kg.

In the t-shirt printing business an ink called Plastisol is often preferred over Super-Opaque because Plastisol Inks do not air-dry at room temperature meaning a printer can print with them all day without any risk of clogging. This means you need to have a mobile heater with a swivel top to dry each finished print layer once you have finished. Personally I don’t like these inks because they have a thick shiny surface which can feel like you are wearing a slab of plastic on your chest. The surface often fragments over time and melts if ironed. Whereas super-opaque inks have a soft surface which fragments less and can also be ironed. 

 

Printing super-cover white onto a roller-colored background

 

Paper Inks

These are used for printing paper or card and are brought pre-mixed. They have a consistency like treacle and like super-opaque inks they always need to be well stirred before use. You can not print them onto fabric.

We use water-based paper inks which are designed to print heavy weight (over 180gsm) papers and cards. To get a good print on a thinner paper you will need to use an oil-based paper ink and these are thicker and much harder to clean up (using turps or thinners).

They are also quite expensive costing between $50-60 per litre.

 

EQUIPMENT

Screens and Meshes

You can get screens made up to just about any size you want, you can make them yourself and you can often pick them up cheap on Trade Me. At Inverlochy we mainly use standard t-shirt/paper screens (size?) which have a working internal area of about A3 size.

 

Screens are covered with plastic polymer mesh. There are a lot of different mesh sizes available. The number of the mesh (usually written on the screen’s frame) refers to the number of holes per centimetre (or inch as some screen products are from the US).

 

 A low mesh number (e.g.30) means mesh with a small number of large holes. Low mesh numbers are best for printing blocky designs without much detail onto fabric.

 

A high mesh number (e.g.120) means mesh with a high number of small holes. High mesh numbers are best for printing very detailed designs on paper.

 

At Inverlochy we mainly use bog standard 43T mesh (why it’s  ‘43’ and not ‘40’ or ‘45’ I don’t know). This mesh size is good for reasonably detailed designs on fabric or t-shirts. If the design is more detailed you may need t get a screen covered in 60 – 80 mesh but if you go much finer than this it is difficult to get a god print on fabric. Because paper is much thinner than fabric much higher mesh numbers(and therefore detail) can be obtained.

 

You can cover old/damaged screens with new mesh yourself using a staple-gun or get them stretched and glued professionally (at Blue Print). If you use a staple gun you need an assistant to hold the mesh taunt while you staple it on. It needs to be firm and not loose to the touch. Once you have stapled it cover the edges of the screen over the top of the staples with masking tape. If you cover a standard sized screen yourself it costs around $15 for the mesh alone whereas Blue Print will recover it for you for between $20-25. (Note a new standard sized screen costs around $40).

Squeegees

Squeegees can be brought from any screen-print supply house. It is good to have a number of squeegees of different blade widths. Squeegees with firm sharp blades are best. The edges can be re-sharpened using sand –paper.

 

Hinged Printing Boards

It is useful to have a large board with hinged clamps attached for printing paper. The screen is screwed into the two clamps so it can be raised and lowered by the hinge. Currently these hinges only seem to be available from CCG(See Supplier List) in Auckland for something around $60+ each.

 

MATERIALS

 

Paper/Card

 

Heavy weight (over 180gsm) un-coated papers and cardboards are best. If I want to do a really nice print on paper I will buy something between 250 – 350 gsm. The more absorbent the paper the easier it is to get a good sharp print. You can buy special heavy-weight linen based printing papers at Art Supply Shops such as The French Art Shop and Gordon Harris for about $10 per A1 sheet (or less then that if you buy it wholesale from Fine Art Papers in Christchurch – See Suppliers). I like to use Imprezioni and Arches.

Fabric

We have already talked about what sort of fabric to print on. Fabrics come in a variety of widths (90cm / 110cm / 115cm/ 2m). If you are going to print fabric is a good idea to have the inner width of your design some ratio of the fabric width (e.g. a 55 centimetre wide design to print a 110cm wide fabric) so you do not end up with a large un-printed (or messy half-printed) surplus.

Check fabrics for a grain and a ‘right’ and a ‘wrong’ side.

Not all fabrics have a right and a wrong side. It is usually only the thicker fabrics (e.g. knit / lycra) where this is important. Check both sides of the fabric. If one side has a obvious grain (‘tiny parallel ‘railway tracks’ ) versus more of criss-cross or net look then this is the correct sign and you should print your design down the length of the grain.

 

PRINTING

 

Print fabrics on a soft surface such as a blanket or thin layer of foam.

Print paper/card on a hard surface using a hinged board.

Find a squeegee that is slightly wider than your design and orientate the screen so that the narrowest side of your design is at the top.

Run a layer of ink about half the width of your finger above the top of your design. Big bold designs (with lots of open holes!) require more ink than fine detail designs (with less open holes).

Put your squeegee down upright (at 90 degrees) above the line of ink and tilt your squeegee about 20 degrees towards you. The narrower the angle of the squeegee the less ink goes through the screen. If you tilt the squeegee towards you too much too much ink goes through and you end up with messy prints and edge lines.

Try and keep the bottom of the blade fairly clean of ink and wipe it if it does become covered. The ink should be on the edge of the blade and not the bottom.

Pull the squeegee towards you as you concentrate on covering the design area evenly with ink. This is your ‘Flood’ stroke.

Then repeat the process. This time you are concentrating on pushing down as hard as you can over the design area. This is your ‘Pressure’ stroke which should force all of the ink from your pressure stroke onto the substrate beneath,

When you are printing paper you should do your flood stroke with the screen raised off the board (see photo below) and then do your pressure stroke (Often with no ink) with the screen down on the board. Do not ‘double flood’. If you fail to flood the whole design area on your first stroke take a little bit of ink with you on your Pressure Stroke.

 

When you are printing fabric do both types of stroke with the screen down flat on the table. Always take ink with you on your Pressure Strokes. If you are printing super-opaque inks you may need to do three flood and pressure strokes to get a good coating. If you have to do more than this you should re-expose your design on a coarser screen.

So the minimum application (for paper only) is -

One Flood Stroke and one Pressure Stroke with No Ink (for paper only)

The maximum (for super-opaque on fabric)  is –

Flood/Pressure with ink

Flood/Pressure with ink

Flood/Pressure with ink

When you have finished scrape off any remaining ink and put it back in the container. Wash both sides of your screen with cold water using a hose or water blaster. The surface of the screen should be wiped using an old scouring cloth rather than a dish-washing brush which may damage your emulsion.

Learning how much ink and pressure to use with different designs on different papers and fabrics is the most difficult part of screen-printing and does take some time to master.

You should always use rubber or latex gloves and have good ventilation.  Try and clean your screens considerately so that the resulting wash goes down interior ‘grey water’ drains (where the solids are leached out) rather than exterior storm drains heading straight into a nearby stream or ocean.

 

SETTING UP

 

 Some of the things you’ll need to set yourself up.

1) Screens – you will need a few – it is best to put every colour separation on its own screen so for a four colour print you will have four screens.

2) Squeegees – It is always good to have a number of different widths on hand. They are expensive – around $60 for a standard size.

3) Spatulas for missing your inks and putting them on the screen.

4) Inks – it depends what you are printing –fabric or paper. At Inverlochy we try to have all of the primary colours available in the standard inks and white/gold/black and red in the super-opaques.

5) Ink additives – Things such as cold cure, ink softeners/additives for printing synthetic fabrics

6) Screen-strip

7)Print Table – Any large table covered with a soft smooth surface such as a blanket or foam carpet underlay is a good surface for printing fabric.

8) Hinged Board – For printing paper

9) Exposure Table – A place to expose your screens. You will need a sheet of glass to cover the screen. (Note – many screen-printers including myself will expose a screen for you of you bring in the screen and transparency. I normally charge $20 to put an image on screen.)

10) Exposure Lamp - A powerful light (e.g. 2- 5 KW) to expose your screens. You can hang this above your exposure table or place it underneath if your exposure table has a glass surface. The light should be placed 50cm – 1m from your screen.

11) Photo-emulsion – buy it by the litre and mix in the accompanying activation powder when you are ready to use it.

12) Jiff – for Cleaning screens

13) Masking tape – for taping up screens/attaching stencils/blocking holes/making registration marks and taping down t-shirts

14) Hose/water-blaster and somewhere to wash your screens.

15) Rags – for clean up.

Wholesale art paper from - http://www.fineartpapers.co.nz/

 

SUPPLIERS

 

 ____________________________________________________

Blue Print – 55 Sydney Street – Petone – Phone 04 – 568 3555

For most of your screen-printing requirements in Wellington.

http://blueprintimaging.co.nz/screenprinting.php

_____________________________________________________

Universal Screen

– Auckland – for stuff Blue Print doesn’t have.

http://www.uniscreen.co.nz/

_____________________________________________________

CCG Industries

–  Auckland - ditto

http://www.ccg.co.nz/

______________________________________________________

Cheap T-shirts can be obtained from - http://www.blanktees.co.nz/about

And  - http://ascolour.co.nz/

______________________________________________________

 

 

 

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