Introduction

What is 2.5D printing? And what is the half-a-dimensional quality that we are attempting to describe? Does it address surface, relief, texture, material? Or about perception, appearance, illusion? Or terms-of reference or taxonomy, or methods of capturing, measuring and modelling material appearance? Or is it about trends and new technologies? The simple answer is that it is all of the above and more. The primary objective of this book is to scope and identify the essential 2.5D qualities and benchmarks. The challenge is how to arrive at definitions and exemplars that - in this rapidly developing and changing technology - effectively reflects the current state of the art of 2.5D printing, and to provide insights into the future of printing and additive manufacturing.

As the title of the book suggests, there are two primary aspects to this enquiry: the dimensional - the need to gain insights and understanding of a surface that is neither 2D nor 3D, but is somewhere in between, and yet can effectively describe the micro and macro textures; the print - how an object, a scene or an image can then be captured, measured, recorded and printed as a physical reproduction. Furthermore, there is also an extra element, which could be considered as the illusive 'x' or an extra half dimension that is much harder to describe. For the purposes of this enquiry, and because it is highly significant for us, it relates to, firstly, the printing processes, materials and colours to create a textured surface, and secondly, its appearance; our human, emotional and perceptual relationship with the printed image.

The Internet has provided access to unlimited images and things we may never have anticipated or known about. Digital technologies have irrevocably changed and challenged the way we look at, construct and print images and objects. We work digitally and incorporate numerous digitally aided technologies as a part of our daily workflow. As we move from real-world texture to screen-based or printed representations of texture, our understanding and engagement is mediated by the screen or printed matrix. Furthermore, colour-printing technologies have evolved from coloured dots on paper to coloured dots on three-dimensional objects. What has remained unchanged are the thin-film CMYK process inks and colours by which images are printed. The next step in colour printing is a modification to the thickness of the film to create a new dimensionality or functionality.

We are also working on the idea that 2.5D printing demonstrates a materiality of surface, which could be described as the relationship of materials, texture and surface. The aim here is to explore ways in which an extra half-dimension can incorporate an idea of otherness, a physical delight, or a visual engagement to imply a mixture of aura, illusion and paradox. We could begin by suggesting there is a halfway point between conscious and unconscious seeing: how do we observe, recall and differentiate thousands of different materials and textures, and, in particular, coloured materials and textures? This materiality of surface can also imply whether we are likely to find a surface or material convincing and whether we are unconsciously drawn to their tactile qualities, or are physically repelled by surfaces, materials and colours.

We are presented with thousands of different textures and materials every day and at a glance we are able to determine each of their material characteristics. Moreover, we are attracted to natural things, and the material qualities of these natural objects, who is not tempted during a walk along a beach to pick up sea-smoothed pieces of glass, wet pebbles or shells? We still like to preserve the analogue - there is renewed interest in vinyl records, analogue film, black and white photography and the rustle of the pages of hardback books. More frequently, we do not have time to engage with everything we see, and therefore it seems that there is more effort to ask someone to stop and look. Walking through a gallery, looking through a picture book or a clever advertisement, how long do we look at an image? Seconds? The challenge therefore is to ensure that images have the potential to arrest the viewer and stop them in their tracks and maybe to take a second look.

As more stuff is created in our increasingly hectic world we need to ensure that the things we design and make are of benefit to our health and safety, as well as provide us with pleasure and comfort. We suggest it is increasingly important to gain an understanding of the entire design process: firstly, that a product is well designed and fabricated and, secondly, the design process does not finish at the manufacturing stage, but continues beyond its lifetime. For example, what happens to the artefact after it is made? Should the materials that we use have a sustained lifecycle and not simply be thrown away? Therefore, the second aspect of this search is to consider the materials that we use: can the printing materials be useful? Save lives? Be eaten? Can they be touched? Do they provide wellbeing, comfort or visual delight?

In preparation for printing we may also struggle to work with materials that are neither aesthetically pleasing nor pleasant to the touch or smell. These materials may have been developed based on the limitations and constraints of the hardware, for example: printers, plotters and cutting tools, and materials: paints and inks, nylons and polyesters. It is, therefore, of inestimable importance that the materials, the processes and tools we use today and in preparation for the future are: of high quality, are pleasing to the eye and the touch, offer new design solutions towards social impacts, provide comfort and wellbeing, for example, and, finally, can ensure a legacy for future generations.

The structure of this book is divided into five chapters. In Chapter 1, we investigate the relationship between material and texture and how each conveys a character or quality. We explore the physical, perceptual, linguistic, natural and artistic interpretations of these appearances. We also consider the relationship between images, pictures and printing, how appearances are reproduced, and the idea that as reproductions, a picture may convey some sort of embedded aura or emotion. In Chapter 2, we study the past: how artists have observed scenes and objects, and used different tools and materials to translate the appearance of textured objects into pictures, reliefs and artefacts. Chapter 3 considers the present, and the range of methods that are being used to capture different surface qualities, and how these are measured, categorised, reproduced and applied in the twenty-first century. In Chapter 4, we suggest future trends and the implications for the print industry. The aim of Chapter 5 is to explore, through different case studies, concepts and ideas about material appearance and methods for reproduction. The case studies are chosen based on our experiences and interests. These include day-to-day objects, artefacts, materials and surfaces, many of which are taken for granted and overlooked, but that in reality represent the sum of efforts in many different creative and technological fields. The case studies may also reflect on a span of history- from ancient to contemporary production. Some case studies may be considered as niche or outdated, but the aim is to demonstrate the enormous variables, materials and crafts skills that could be used as benchmarks when considering the specifications of a design and production workflow. It may be obvious by now, but our examples are focused in aesthetic applications as they display the capabilities and the full potential of relief printing as a digital tool. We have used these case studies to explore and consider how manufacturers have adapted methods to incorporate new materials, technologies, and responded to emerging consumer trends.

Before we can embark on the '2.5D-ness' of a surface, we would firstly like to consider what does 2.5D really describe or imply? In essence, the question is what do we mean by 2.5D? What are the qualities that define it? One can start with a negative and suggest that it is not about printing objects (3D) or about printing images (2D), but something between the two - or more simply put: what is the relationship between the textural attributes of a material and the object? The important factors in gaining an understanding of 2.5D are:

• To identify the key terms,
• To address assumptions,
• To establish the relationship between perceptual and physical (visual, tactile and physical),
• To look back to existing historical benchmarks,
• To survey contemporary making,
• To identify current weaknesses and problems,
• To demonstrate current emerging ideas that could lead to further exploitation,
• To set out a series of benchmarks and objectives in need of addressing.

The underlying motivation is to ask 'why, what and how?' The rationale underpinning the book 2.5D Printing has evolved through personal interest and our research in working towards developing methods that: capture, measure and model the surface qualities of 3D and 2D objects, as well as those that represent and reproduce the appearance of surface, materials and textured qualities. Therefore, with cross-disciplinary understanding and insights in arts and technologies, this book could be considered as a confluence of ideas, methods and applications that investigates the relationship between two and three dimensions. The subject...