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Acrylic Resist Etching: Research & development Suitable safe mordants for biting copper & zinc. Formulas for Acrylic Hard Resist and/or Aquatint: suitable for use on copper & zinc, using various mordants. Materials & techniques using acrylic resists. Exploring health & safety and environmental issues. Elimination of solvents & harmful chemicals from the studio. Replacement with water-based products or safer chemicals. Sourcing suitable materials, equipment & services to develop acrylic resist facility. Design & development of studio facilities. Promoting outcomes from research through education, both in-house and in other studios & educational establishments. Publishing information sheets, technical articles, etc. Photopolymer Printmaking: Research & development Sourcing suitable products for studio use. Study of relevant published information on products and processes. Comparing and contrasting products available. Exploration of methods of producing positive transparencies: hand-drawn, photographic and digital. Sourcing materials & services. Exploring health & safety and environmental issues. Establishing safe and successful work practises for lamination, exposure and development. Documentation of research: through information sheets, technical articles, etc. Education: through a programme of workshops both in-house and in other studio facilities. Future research Further development and improvement of present etching systems and products. Sourcing new photopolymer products for trial and evaluation. Exploration of printing techniques. Sourcing and developing suitable inks. Documentation & publishing of research. New avenues and new materials – in collaboration with publishing programme. Acrylic Resist Etching & Polymer Photogravure
The following material is intended only as an introductory guide to these techniques and was written by Alfons Bytautas ARSA, Senior Etching Technician at Edinburgh Printmakers. He has held numerous workshops in Acrylic Resist Etching and Photopolymer throughout Scotland and abroad. Workshops have been held at the Amsterdam Graphic Atelier and at the Frans Masereel Centre in Belgium where he was invited as guest speaker at a symposium on 'Printmaking and Ecology'. In 1994 he was elected an Associate Member of the Royal Scottish Academy and has been a Visiting Lecturer at the University of Northumbria since 2000. The changing face of etching & intaglio printmaking
Edinburgh Printmakers has always welcomed change and, with increased awareness of the issues of health and safety associated with printmaking, we began to consider ways in which we could make our working environment healthier and safer. Since 1994 we have utilised safer etching systems - getting rid of hazardous chemicals and solvents used in the technique of etching. At EP we’ve eschewed the terms “Non-Toxic Printmaking” or (worse still!) “Safe Etching”. We feel these terms are misleading. Although a few of the materials we use are certified “non-toxic”, the majority are still potentially harmful if misused. We always insist users wear suitable protection and follow the correct procedures when working with these techniques. We were the first to refer to the system as “Acrylic Resist Etching”. This encompasses a wide range of techniques using water-based etching resists. We’ve developed our own recipes based on years of experience, encouraged by a willingness to experiment. These resists are easy to use, clean up with water and are amazingly versatile. At present we use copper and zinc plates for etching. We etch the copper in vertical dip-tanks containing ferric chloride. Zinc plates are etched in ferric (not Edinburgh Etch!) or copper sulphate. Once the plates are etched and printed, the prints look exactly the same as those produced by so-called “traditional” methods. Using water-based resists means cutting down or eliminating the need for solvents - the studio is a happier and healthier place. We also use photopolymers extensively for both photo etching and “non-etch’” polymer photogravure. We use “Photec”, a photopolymer film that can be laminated onto metal plates and etched. For “non-etch” we use the same film or Toyobo KM95R flexigraphic plates. Both can be used in an astonishing variety of ways working from hand-drawn, photographic and digital artwork. The flexigraphic plates are particularly useful for our editioning programme here at EPW as we can print large numbers from the processed plate. Unfortunately many artists seeking to use our facilities have received little or no training in these methods (though they are now being widely adopted both in the UK & worldwide). This means that we positively encourage prospective users to undertake appropriate training with us before using the studio to guarantee safety for themselves and others. We have also worked with other studios and university printmaking departments in the UK and abroad to help them establish these safer working methods. These include: Taigh Chearsabhagh Museum &
Arts Centre, Lochmaddy, North Uist, Scotland. Acrylic Resist Etching
Etching is an intaglio printing process. Intaglio means a figure or a design cut or hollowed out of any substance. In the technique of etching a metal plate is covered with an acid-resistant layer and the design is scratched through this layer or “ground”, which exposes the metal. The lines can now be corroded or “bitten” into the plate using acids. Nitric acid has been most commonly used to bite plates. When the biting process is complete the ground or resist is removed from the plate and the plate is ready for inking-up. Traditionally resists were composed of materials such as beeswax, asphaltum and pitch and had to be removed with solvent (white spirit / turpentine substitute). However today more artists are aware of the potential health hazards associated with traditional printmaking materials. Instead of using dangerous acids we now use much safer corrosive salts to bite the plates. Acrylic resist etching replaces solvent-based systems with water-based products. Already several commercially produced acrylic resists are available from specialist suppliers. The idea of using acrylic polymer varnishes instead of solvent-based resists is not really new and it is relatively easy to manufacture a reliable etching ground from a wide variety of products available today. For line etching we currently use an etching resist that we make ourselves. The main constituent of the “Hard Resist” is an acrylic floor shine, “Klear”, manufactured in the UK by S. C. Johnson. Check out the website: www.jwpeurope.com for product listings and availability. As an etching ground “Klear” works well on its own on copper, if the plate is bitten with ferric. We have found that we have had to experiment with a cocktail of various acrylics to produce a reliable resist for etching zinc with copper sulphate. A good resist can also be sprayed onto the plate as an aquatint with little or no modification. Acrylic resists are also available from printmaking suppliers (such as Lascaux Hard Resist, Z-Acryl, etc.). Generally it is cheaper and more fun to mix up your own. Applying the resist To lay an acrylic etching ground it is essential to apply as thin and even a coat of resist as possible. Perhaps the simplest and easiest way to do this is to begin by pouring a sufficient amount into a plastic tray that will fit the size of your plate. Prop the tray up at an angle and pour the resist in to the bottom end. Place the plate in the tray, pick it up and tilt it in the opposite direction so that the resist flows over the surface of the plate. Do this gently to avoid creating bubbles (acrylic polymers contain soapy emulsifiers to enable its constituents to mix) and prop the tray up again. Pick the plate up carefully by the edges, making sure you don’t accidentally mark the face. Hold it up and allow any surplus to drain off into the bath. If the ground doesn’t cover the edge of a plate properly, use a finger to encourage it to flow. After a minute or so “walk” the plate on old blotting paper or newsprint to get rid of any further excess and to prevent a thick line of ground forming at the bottom edge. Place in an upright position for a few minutes, allowing the resist to even out and to dry. Finally it can be dried using warm air (hair drier or fan heater). To coat large plates you may have to pour on the resist. You can catch the excess by placing one end in a tray. Alternatively the resist can also be painted on with a sponge brush. Apply this as you would a wash of watercolour. Prop up the plate and paint carefully from the top allowing the resist to flow downwards as you paint. Drain and dry as before. Wear vinyl catering gloves or non-sterile surgical gloves when coating the plate. Take care so as to avoid splashing – particularly avoiding eye contact. The resist will stain clothing, so take care. For line work the image is drawn using a point – in other words a conventional etching needle. Make sure your needle is sharp enough and whilst excessive pressure is not needed, make sure you use a firm but gentle pressure in order to penetrate the ground. Although we add colour to the resist, the resulting line may be difficult to see for some. It is possible to darken the ground by painting on a thin layer of black gouache. This quickly dries to a matt finish. We use other materials as resist in combination with the “Hard Resist” or on their own. Graphic Chemical Water-based Relief Ink (Carnation Red) is used as a “wet ground”, an alternative to traditional soft ground. As we continue to experiment with these resists we are finding new and exciting ways of working. Acrylic resist etching is not merely a safer alternative to “traditional” etching but is a new technique in itself. Etching the plate: Safety first
Traditionally plates were bitten using acids – either nitric acid or a mix of hydrochloric and potassium chlorate. Needless to say there are considerable risks involved in using such dangerous chemicals. Safe handling and storage is a must as is good extraction and ventilation (this can be costly!). The alternative is to use either ferric chloride or copper sulphate as these produce little or no harmful fumes. Using Ferric Chloride (For Copper) Ferric chloride is a corrosive iron salt solution and was used in the past as an etching solution, principally in the printing industry and for the technique of photogravure. Although it still must be regarded as a potentially harmful chemical, it is much safer to use than acid as it produces no dangerous fumes or noxious odours and is not absorbed through the skin. It is ideal for use with copper and with a little care can also be used to etch zinc (it should not come into contact with aluminium as dangerous reaction can ensue). On the negative side the biting action produces a deposit of iron oxide that can slow down the process and ferric stains everything it comes into contact with (especially clothes!). To overcome the sediment problem there are two easy solutions. Plates can be bitten face up in a tray (the old trick was to bite them face down) but should be removed every 20 minutes or so and washed with cold water. Alternatively they can be bitten in a vertical dip tank. Here the plates will have to have plastic strips taped to the back or the tank will require a special plate holder. To ascertain the strength of your ferric you can use a device known as a hydrometer and “pure” ferric will read 45 degrees Baume on the scale. To do this pour some ferric into a measuring cylinder or deep jug and the hydrometer will sink or float according to how much water is in the mix. It is important to know that the water frees up the free acid (hydrochloric) in the ferric and makes it stronger not weaker. A fast solution will be in the region of 30 degrees. A solution at 42 degrees will be slower but more accurate, producing little widening of the line during etching. Biting plates in corrosive is still a potentially dangerous activity. Wear gloves and goggles and avoid any activity that produces splashes. A heavy-duty plastic or rubber apron will help protect clothes. Ensure that plates are rinsed thoroughly front and back with cold water after etching. If using plastic strips when etching in a dip tank, remove the strip by placing the plate in a tray of cold water and when submerged, gently pull the strip from the back of the plate. Plates should be gently dried by blotting or with warm air after rinsing.
Using copper sulphate as an etching solution for zinc is safe and easy. With some modification the mix can also be used to bite aluminium. (Be aware that aluminium must never come into contact with ferric chloride as a violent chemical reaction may occur!) The solution is mixed from Copper Sulphate crystals. This chemical is variously referred to as Copper Sulphate, Copper Sulphate Pentahydrate or even Copper (111) Sulphate - 5 - Water. Ask for General Purpose Reagent or Industrial grade when ordering. The crystals are mixed with water and gloves and a suitable dust-mask must be used when preparing the stock solution. There are various recipes for differing strengths of mix from 250 grams per litre (strong) to 25 grams per litre (weak). We mix up a strong stock solution and then further dilute it as necessary - mix 250 grams with 1 litre water for the stock solution. Then prepare a bath by adding 500ml of the copper sulphate mix to 500ml of water. This can be further diluted for delicate bites and for aquatints. Be aware of the potential hazards of using the solution - use gloves and wear goggles or avoid eye contact. Copper sulphate residue is a potential hazard to marine life - take precautions and avoid pollution when rinsing the plate or when disposing spent mixes. When biting, the reaction will form a dark coppery coloured residue. This should be brushed off with a sponge brush. If you are using a relatively small tray for etching, the solution should be carefully poured off into another tray and the residue sluiced out with clean water into a bucket. Allow this to settle and then follow these steps. Add sodium carbonate (washing soda) to the solution to neutralise it. Test with pH indicator paper- it should read between 7.0 and 8.0. Allow the copper and zinc hydroxide to settle as sludge and once this has happened, the liquid should be poured off and further diluted prior to disposal. The solid waste is collected in plastic bags and disposed of according to local regulations. Removing the resists After etching, the resists can be removed (or “stripped off”) using a strong solution of household soda crystals (this is sodium carbonate decahydrate – don’t confuse this with caustic soda/sodium hydroxide, which is a dangerous alkaline solution!) Mix approximately 200g soda crystals to1 litre water for a stripping solution and wear gloves and goggles when using. You could also add detergent (soap flakes) to the mix. Soda crystals are available in most supermarkets - either in the 'laundry' or 'cleaning' sections. If biting aluminium with copper sulphate, you may want to consider using sodium metasilicate as the stripping solution for the acrylic resists – soda crystals will etch aluminium! Mix 50 grams of sodium metasilicate with1 litre of water. Further dilute as necessary. Otherwise purchase “Carefree” Stripper (S.C. Johnson) and follow the instructions regarding dilution. Use this product rather than the Speed Stripper as this contains potentially harmful chemicals. Making an Impression: Printing the plate
Although armourers had used the technique as a means of decorating weapons, etching as a printing technique only began in Germany in the 1500’s. Then printing began by grinding black pigment with sticky copperplate (burnt linseed) oil to make ink. This was a particularly laborious task. To print the plate it is first covered with the ink that is forced into the bitten lines with a roller or leather-covered pad known as a dabber. The printer then starts to wipe the plate using muslin-like material. The ink on the top surface of the plate is wiped clean and in doing so, ink is dragged into the lines corroded by the acid. To print etchings, the paper (normally a high-quality acid-free rag paper) is soaked in water and then blotted. Printing on dampened paper ensures that it is soft and pliable and so will take a good impression from the inked-up plate. The printing press (the earliest were made of wood) consists of a plank or “bed” that runs between two rollers, above and below. This action results from the printer pulling on wooden spokes or levers or in later presses, from turning a geared wheel. The printer places the inked-up plate on the press “bed’ and puts the paper on top. A number of fine woollen blankets are placed on top and then plate and paper, cushioned by the blankets, are driven through the press. The pressure forces the paper into the ink-filled lines cut into the metal by the action of the acid during the biting process. The print is then peeled off the plate and the print is dried and flattened by placing it between blotters and absorbent boards. To make another print (sometimes referred to an “impression”), the plate is inked up once more and the whole process repeated. Remarkably little has changed in the way etching plates are wiped and printed although we are beginning to see the introduction of water-based etching ink. Polymer Photogravure & Photo-etching Photography in printmaking
Photography has always been closely linked with printmaking – in 1852 William Henry Fox Talbot began his pioneering work on photographic engraving. He used photosensitised gelatine applied directly to a plate prepared with an aquatint ground. An image was created on the plate by contact exposure; a positive transparency (or a natural object such as a leaf) was placed on the plate and exposed to sunlight. Parts of the coating that had been exposed to the sun were hardened while allowing the soft gelatine, shielded from the light by the positive, to be washed away with water to expose the copper. The plate was then etched and Fox Talbot was the first to use ferric chloride for this process. Interestingly he also experimented with pre-exposing the plate to a "halftone screen", using layers of fine gauze. In 1879 Karl Klic in Vienna ingeniously combined the innovations of Fox Talbot and others in a technique now known as photogravure. A sensitised gelatine coating on paper was exposed and transferred onto an aquatinted copper plate. This was developed in warm water and etched in ferric chloride, in baths of differing strengths. The ferric gradually penetrates through the soluble gelatine, enabling a wide range of tones to be bitten into the plate. The copper plate was then inked, wiped and printed on an etching press. Photo etching is a modern related technique using photosensitive acid resists that are poured or sprayed onto the plate, exposed then etched. The Development of Photopolymer Printmaking Polymer Photogravure
Photogravure was adapted for
commercial use as “rotogravure”, printing from etched copper
cylinders. A related process was “flexography”, using flexible
plates moulded in relief. In the 1960’s rubber plates began to be
replaced by nylon resin polymers. Today photopolymer “flexo”
plates are used extensively for high speed printing in the packaging industry. Some printmakers, such as Eli Ponsaing in Denmark and Dan Welden in USA, realised that photopolymer “flexo” plates could be used for photo-intaglio printmaking. The polymer reacts to ultraviolet light in much the same way as sensitised gelatine in gravure printing. When exposed to continuous tone artwork and printed as intaglio plates, they can produce prints comparable in quality with traditional photogravures. This new printing plate does not involve the use of acids or other hazardous substances in use. It develops simply in water and is therefore very safe to handle and use. Preparing the artwork As we are making a contact exposure, we need to begin with making a full-size positive (not negative) image on transparent or translucent material. Photographic images can be used and positives can be made in the darkroom on various types of film or produced digitally using computer scanning. The density and resolution of the positive image is crucial to the making of a high quality gravure print. The artwork can also be hand-drawn, using a wide variety of drawing materials and techniques ranging from simple crayon drawing to complex mixtures of painted tone and texture. In this case the image is generally produced on a special grained sheet of film (such as True-Grain) although tracing paper could be used with crayon, charcoal, pastel, etc. Exposing the plate
At Edinburgh Printmakers we use Toyobo KM95R Water Washable Plates, exposed on an ultraviolet unit with a single 2-kilowatt light source (preferable to banks of tubes). Unexposed plates can be handled and cut safely in subdued light. First it is important to remove the transparent top sheet from the plate – this comes away easily. The film positive is then placed in contact with the plate (preferably using a vacuum) and is exposed to ultraviolet light. Ensure that artwork and plate are "emulsion to emulsion" – image side against the polymer layer. To find the correct exposure, make a test strip – begin by taping the artwork and plate securely to the glass of the unit and using a piece of black paper, gradually reveal more of the plate as you expose it in stages. During exposure, light passes through areas of clear film hardening the polymer. The opaque material of the image allows little or no light to pass through and these areas remain soft. When developing with water these are washed away, "etching" the image into the polymer. With underexposure, too much will wash away and the resulting image will be dark and ill defined. With overexposure, the polymer will harden too much and the resulting print will be faint with little or no detail. Screen Exposures With hand-drawn artwork or continuous tone positives the plate is then exposed to a random dot or "stochastic" screen. This creates a “grain “ structure, which necessary for holding the ink, especially in solid black areas. Our digitally made screens have an extremely fine aquatint-like structure. To find the correct exposures, step tests are made combining several steps of the image exposure (running horizontally on the test plate) with a couple of different screen exposures (vertical steps). Following on from the image exposures, the artwork is removed (keep the plate face down on black paper or in a folder to avoid unnecessary exposure during the changeover) and the dot screen placed on the unit. The matt emulsion side of the screen is in contact with the polymer (remember "emulsion to emulsion"!) and one half of the plate is masked off with black paper prior to making the first exposure. After this, turn the plate around and make a new screen exposure, perhaps doubling the time. Finding the correct exposures is time consuming but once you have ascertained these, the process becomes relatively easy. There is reasonable latitude when it comes to exposing the plate – polymer plates need much more exposure than a film such as Imag-On Ultra. Developing
After exposure, the plate is ready for developing. This is safe and simple – begin by filling a tray with water at approximately 25 degrees Centigrade. Don’t guess; use a thermometer! We develop in three stages, each lasting a minute. Wear gloves to avoid contact with dissolved polymer. One – place the plate in the tray of water and let it sit for one minute. Two – remove and gently rub the surface of the plate with a sponge under running water (preferably at 25 degrees) for one minute. Alternatively do this with the plate still in the tray. Three – hose the plate with water for a further minute. The plate is quickly dried using paper towels to gently blot the surface. Change the towels frequently and once it seems to stick gently to the surface when the water has been mopped up, dry the plate with gentle heat. After approximately 10 minutes the plate loses its stickiness and is ready for a final exposure to ultraviolet to harden the polymer for printing. Timing is not crucial but ensure that this exposure is at least as long as the image exposure. The plate is now ready for printing, though you could rub vegetable oil on it before inking up for the first time (to ensure that it doesn't stick to the printing paper). Tips for printing
For printing, choose a soft responsive paper; Hahnemuhle Etching is ideal. The paper is soaked and dampened as usual. Use Graphic Chemical Easy Wipe Compound or weak copperplate oil in your ink when mixing to ensure it isn’t too stiff. The plate will scratch easily if there is any grit, so take care when inking up. Experiment with adding Extender/Transparent White as this increases the tonal range and can improve an otherwise murky print. The plates generally wipe easily, requiring soft scrim and a paper wipe with little or no heat. As the edges can’t be bevelled, we usually have a margin round the image and print using a plastic mask with an aperture cut to the image size. You may need to adjust the pressure of your press; try printing with reduced pressure first. With traditional inks, clean the plates with vegetable oil and finish with a little low-odour turpentine to remove any traces of oil. Use the same procedure with water-based inks, as water will now damage the polymer. Plates are stored wrapped up, preferably in a dark cupboard in a dry area.
Photopolymer films have two properties that are of interest to us as printmakers. First, they are sensitive to ultraviolet light and can be exposed using various UV light sources including sunlight. Second, they are extremely acid-resistant and when used as a photo-resist, even the finest of detail can be subjected to lengthy biting. Various types of film are available – Photec, Imag-On Ultra and Pure Etch are ones we have tested. These films were developed for the production of printed circuit boards. Being a product for the printed circuit industry, these films are available in large rolls, often packaged in pairs. The polymer itself is light blue in colour and is sandwiched between two layers of clear plastic film. The inside protective layer is soft, resembling polythene, while the other layer is a more brittle cellophane-like material. Mark Zaffron and Keith Howard, who introduced us to photopolymer during a workshop held at Edinburgh Printmakers in 1994, pioneered their use in photo etching and photo-intaglio. Since then, with the expertise and hard work of our members and staff alike, Edinburgh Printmakers Workshop has continued to research and develop this exciting new form of printmaking and has become recognised as one of the leading studios using this technique. The technique is similar to that of polymer photogravure but plates can be exposed for conventional etching or the polymer itself forms the printing matrix in what we refer to as “non-etch” techniques. A Quick Guide to using Photopolymer Film
1) Plate edges should be filed. Prepare the plate by degreasing. Use a kitchen scourer and scrub the metal plate, as this will create a slight tooth to help the film stick evenly. Rinse front and back with warm water and dry under the hot-air drier. The plate can also be sprayed with a fine acrylic aquatint, as this will also help the film adhere. Ensure the aquatint is dry before moving to stage 2. 2) Cut the film to size allowing a small margin all around the plate. Do this in subdued light or in a darkroom (yellow safe light). 3) Strip off the first protective layer. The film has a natural curl - work with the film curl side uppermost. Attach sticky tape to one corner and peel back. After removing this layer, the film lies flat. Place the film in a lightproof folder to protect it. 4) Laminate the film onto the plate using the etching press. This should be prepared by placing a sheet of Perspex or similar material on the bed. Ensure that this is clean and free from scratches and set the press at the right pressure to accommodate this. Remove the film from the folder and place onto the perspex with the stripped-off side uppermost. Place the plate onto the film and put a sheet of newsprint over the plate. Bring down the press blankets over the plate and run through the press slowly and evenly. 5) After removing the blankets and newsprint slip the plate back into the folder. In safelight conditions trim the excess film off. It's easier to do this face down, using the edge of the plate to cut against. Dispose of any scraps. 6) Use the UV unit to make the exposure (or sunlight, if this is not available). Read the section on exposing the plate in “Polymer Photogravure” for more information on this. Place the artwork in contact with the photopolymer. For an etch exposure, expose to the image only. “Non-etch” exposures will need a screen exposure, using the “random dot” screen. 7) After exposure, slip the plate back into the folder and return to the darkroom and work under yellow light. The remaining top layer of film must now be stripped off. Place the plate face up in a tray of developer. To make the developer use 10g of soda crystals mixed with 1 litre of water - use at a temperature of between 20-25 degrees Centigrade. 8) Allow to sit for ten to thirty seconds for an etch exposure or one minute for “non-etch”, then gently sponge the plate allowing for a total development time of two minutes. 9) Now rinse the plate with cold water and use a squeegee to remove water. Blot dry with a paper towel. Ensure no water is left on the plate and leave to dry. Gentle heat can be used to speed dry. 10) If you’re etching the plate, when the plate is dry try test bite it in the ferric or copper sulphate bath, depending on which metal you’re using. Bitten areas will darken. Return to developer if not fully developed. Rinse, dry and test again. Once the plate is biting as desired, after rinsing with water and drying it, harden the polymer by exposing it to ultraviolet again. Make this as long as the main exposure and a little more. You could also place the plate in sunlight outdoors until the polymer darkens in colour. 11) ‘Non-etch’ plates should also be hardened before printing. To avoid the plate sticking to the printing paper, rub with a little vegetable oil prior to printing for the first time. 12) If you wish to remove the polymer, immerse for at least 5 minutes in a stripping solution. Rinse thoroughly and dry.
Intaglio Printmaker Lascaux Hard Resist / Liquid
Hard Ground 500ml Lawrence Ferric Chloride Crystals
550gm/5kg Edinburgh Printmakers Photec Photo-polymer Film
(per metre) Specialist Equipment & Services Richards of Hull Specialist suppliers of Vertical Etching/Stripping Tanks, Plate making Sinks, Ventilated Acid Units, etc. Inks Hawthorn Printmaker
Supplies Supplies Non-skinning Etching
Inks 450/225 gm tin Paper John Purcell Paper True-Grain Polyester Drawing
Film (Sheet: 80x122cm / Roll 123cm x10m) Links Frans Masereel Centre,
Belgium Amsterdams Grafisch
Atelier, Netherlands Taigh Chearsabhagh
Museum & Arts Centre Printmaking Today
The Sidney Nolan Trust
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