This is a set of 42 original 6x6 slides depicting the surface / atmosphere of the unknown planetoid where the Nostromo crew discovers the Alien derelict.
These photographs were taken by Dennis Lowe, credited as a special effects technician on the film.
Each of these slides is totally unique.
Among them is the one used in two important shots : one of the refinery orbiting the planetoid (also known as the "2001 shot" among the crew) and another of the Nostromo approaching the planetoid. (it's not that obvious but the same slide was also used in the opening credits)
Dennis Lowe created these amazing photographs using an inovative and rather simple technique inherited from his Art school years: He dropped aluminum paint on a tray of white spirit, then properly lit the amazing textures that merged in the process and shot them using an Hasselblad 6x6 camera.
The slides were later front projected on spherical or semi spherical objects in order to distort them properly and give the final effects a planet surface / atmosphere look. The result on screen is simply stunning and adds a lot to the mood of the space scenes where the Nostromo and its refinery are seen approaching then orbiting the planetoid.
The slides composing this set were acquired from two different sources and are in pristine condition.
The fourth image shows two photos of Dennis Lowe (+ fellow crew member Jon Sorensen and Special effects supervisor Nick Allder) at work with the 6x6 camera and the tray of white spirit. You can also spot blank spherical shapes in the background, probably the ones where the slides were later front projected to achieve the aforementioned orbit shots.