Participation in the Neoconcrete non-object took different forms. Oiticica, for example, extended the idea of corners and folds to be peered into by the viewer in hanging works such as his ‘Spatial Reliefs’ or the 1960 ‘Nucleus’ by using a box format in his later ‘Box Bólides’ (translatable as ‘Box Fireballs’), painted wooden boxes with varying numbers of hinged doors, internal partitions or drawers. In these works, viewers are invited to open and close the hinged doors, handle the boxes, look into corners and sometimes through holes. The 1964 ‘Box Bólide 9’ contains panels and drawers which can be slid horizontally, one of them containing bright yellow pigment, contrasting with the painted orange box. According to Guy Brett, the Bólides’ ‘ways of opening are puzzling, and their insides are remote like the insides of caves.’ Moreover, in works such as ‘Box Bólide 9’, the ‘presence of a natural element loose in the kind of space [where] we normally keep small possessions is quite bewitching.’ More surprisingly perhaps, Yve-Alain Bois remembers that when confronted with Judd’s works he ‘couldn’t shake off the titillating impression that his boxes harboured some kind of “secret.”’ Puzzling, bewitching and titillating, both Judd’s and Oiticica’s boxes seem to invite an intimate relationship in which viewers can establish a close connection between their bodies and these special objects; their boxes allow viewers to access the empty cores of their shell-like forms, appealing to the viewer’s curiosity and staging experiences of anticipation and surprise. Hilton Kramer’s humorous description of Judd as a ‘closet hedonist’ not only emphasises the sensual dimension of his work: the image of the closet situates the pleasure involved in viewing these objects at the threshold between inside and outside, hidden and visible, private and public.
Secrecy and mystery were also associated with Clark’s ‘Bichos’ in early descriptions – one critic even called them ‘diabolical’, because the discovery of their secret geometric structure is usually frustrated by their spatial complexity. Gullar stated that Clark’s ‘Bichos’ exist like ‘mirages’ rather than images, and Bois has also spoken of the ‘mirages’ in Judd’s works, as light and reflections often play disorienting tricks with our perceptions. This aspect of Judd’s work has often been seen as contradicting his emphasis on clarity – as Rosalind Krauss explained in 1966, ‘the strength of the sculpture derives from the fact that grasping the works by means of a list of their physical properties, no matter how complete, is both possible and impossible.’ For Krauss, this discrepancy is precisely what characterises the phenomenological perception of the object described by the French philosopher Maurice Merleau-Ponty: a perception in which the gaze does not grasp the object through an intellectual act, but rather through an embodied, changeable, temporal, inexhaustible process. That Merleau-Ponty’s 1945 ‘Phenomenology of Perception’ was a key reference for Gullar and the Neoconcretists explains why they too were interested in what they called ‘the eye-body’ – an experience of objects contingent on a lived space and time.