Films first black

Of these methods, the first can give accurate values of the mean film thickness only in the absence of surface waves. The fourth and fifth methods can be used only for the mean film thickness, while methods (2), (3), (6), (7), and (8) may be used for measuring either the local or mean film thicknesses. Black (B12) and Portalski (P4) have discussed the advantages and disadvantages of most of these measurement techniques, and Hewitt and Lovegrove (Hlla) have compared the film thickness values measured by three different methods. 

We have seen that full color perception can be achieved by subtraction methods using dyes in suitable combinations. We now have to consider how such dyes are formed on exposure and development of color film. First though, you should recognize that a photographic emulsion, whether for color or black-and-white film, is light-sensitive primarily because of the presence of silver halide. You will recall from previous discussions (Section 26-2C) that the sequence from exposure to development involves the following ... 

The observed equilibrium thickness represents the film dimensions where the attractive and repulsive forces within the film are balanced. This parameter is very dependent upon the ionic composition of the solution as a major stabilizing force arizes from the ionic double layer interactions between any charged adsorbed layers confining the film. Increasing the ionic strength can reduce the repulsion between layers and at a critical concentration can induce a transition from the primary or common black film to a secondary or Newton black film. These latter films are very thin and contain little or no free interlamellar liquid. Such a transition is observed with SDS films in 0.5 M NaCl and results in a film that is only 5 nm thick. The drainage properties of these films follows that described above but the first black spot spreads instantly and almost explosively to occupy the whole film. This latter process occurs in the millisecond timescale. 

Watch the portion of The Wizard of Oz in which the film changes from black and white to color. Explain why you think the film was made in this manner. Discuss the use of black and white and color in other films you have seen (e.g., why do you think that Schindler s List was first filmed in black and white and later filmed in color ). 

Data on emulsion film formation from insoluble surfactant monolayer are rather poor. It is known, however, that such films can be obtained when a bubble is blown at the surface of insoluble monolayers on an aqueous substrate [391,392]. Richter, Platikanov and Kretzschmar [393] have developed a technique for formation of black foam films which involves blowing a bubble at the interface of controlled monolayer (see Chapter 2). Experiments performed with monolayers from DL-Py-dipalmitoyl-lecithin on 510 3 mol dm 3 NaCl aqueous solution at 22°C gave two important results. Firstly, it was established that foam films, including black films, with a sufficiently long lifetime, formed only when the monolayer of lecithin molecules had penetrated into the bubble surface as well, i.e. there are monolayers at both film surfaces on the contrary a monolayer, however dense, formed only at one of the film surfaces could not stabilize it alone and the film ruptured at the instant of its formation. Secondly, relatively stable black films formed at rather high surface pressures of the monolayer at area less than 53A2 per molecule, i.e. the monolayer should be close-packed, which corresponds to the situation in black films stabilized with soluble surfactants. 

In the earliest days of motion pictures, color film had not yet been invented. Some films were colorized by hand, but that soon proved impractical. Color film first came out in the mid-1930s. It used three layers of colored film to reproduce the visual spectrum. Because color film was expensive and required precise control of lighting, black and white film remained the standard until the mid-1950s. Color and black-and-white were both used until the late 1960s, when color became the standard. This was partly because many films were sold for television broadcast after appearing in theaters, and black-and-white films were much harder to sell for television. 

The critical thickness value at which the CF ruptures (due to thickness perturbations) fluctuates, and an average value may be defined. However, an alternative situation may occur as is reached and instead of mpturing a metastable film (high stabihty) may be formed with a thickness hobserved experimentally through the formation of islands of spots which appear black in light reflected from the surface consequently, this film is often referred to as first black or common black film. The surfactant concentration at which this first black film is produced may be one to two orders of magnitude lower than the cmc. 

At a sodium chloride concentration of 10 2 mole/dm3, two coexisting films were observed the thicker, first black, was ca. 85 A thick. With a further increase in salt concentration the thickness of the first black film decreased until it reached 60 A at a salt concentration of ca. 5 X 10 1 mole/dm3—i.e., it became a second black film. 

The equilibrium thickness of foam films drawn from solutions of DMS containing potassium thiocyanate at various concentrations are shown in Figure 2. In this case first black films were formed with a thickness of 975 A at a salt concentration of 4 X 10"4 mole/dm3. The thickness decreased with increasing salt concentration and reached 59 A, those of a second black film, at salt concentrations of the order of 0.5 mole/dm3 potassium thiocyanate. 

The remarkable similarity between the sodium chloride concentration at which the mobility obtained a reasonable value and that at which a first black film was formed suggests that at this concentration chloride ions adsorb to the sulfoxide groups and thus produce a potential which can provide electrostatic repulsion between the monolayers in the soap film. In the case of potassium thiocyanate, adsorption appears to commence at a lower salt concentration, suggesting a stronger free energy of adsorption for the thiocyanate ion and consequently a greater extent of adsorption. Thus a higher potential would be obtained at the interface. 

The films formed from potassium thiocyanate solutions behaved differently from those formed from sodium chloride solutions. At the lowest salt concentration examined, 4 X 10"4 mole/dm3, the film had a thickness of 975 A, clearly a first black film. With increasing salt concentration the film thickness decreased and reached 60 A at a thiocyanate concentration of 5 X 10 1 mole/dm3 it remained at this thickness as the salt concentration was increased to 1 mole/dm3. This corresponded to the second black film thickness obtained with the films in sodium chloride solutions, and in this state the films were quite stable. The considerably thicker films formed in the presence of the thiocyanate ion indicate a stronger double layer repulsion effect than with chloride and hence a stronger adsorption of the thiocyanate ion to the film surface. These re-... 

The overall results show that electrostatic factors lead to the formation of first black films from non-ionic surface active agents in electrolytes and that zeta-potentials as low as 18 mV are adequate to stabilize the film assuming the film potentials are comparable with those of the emulsion drop. As shown in more detail elsewhere, the DLVO theory can be used... 

The film eventually reaches an equilibrium thickness in which both faces of the film are parallel (Fig. 1.18(c)). In this state there is no variation in intensity over the surface of the film. This is called the common black film. It occurs, typically, at a thickness of 300A (30nm). A further decrease in the film thickness, to another stable equilibrium state with a thickness of about 50A, is often possible and is known as the Newton black film. This film is darker than the first black film, the common black film, as the second of the two split rays, that is refracted into the film, travels through a thinner soap film than in the case of the common black film. Consequently the phase difference between the two split rays of the Newton black film is closer to tt than in the case of the common black film. Some films have only one equilibrium state while others have two or more equilibrium states. 

One case, that of a black film, is particularly important Soap films, which are thirmer than 30 nm appear black [718, 749, 750, 752]. Newton was the first to have reported on black films. Very thin films appear black because the light reflected from the backside is phase shifted by X/2 and the path length in the film is negligibly small. For this reason, the phase difference between the two rays is k/2 and they interfere destructively. No light is reflected and the film appears black when viewed against a black background. 

Properties. Uranium metal is a dense, bright silvery, ductile, and malleable metal. Uranium is highly electropositive, resembling magnesium, and tarnishes rapidly on exposure to air. Even a poHshed surface becomes coated with a dark-colored oxide layer in a short time upon exposure to air. At elevated temperatures, uranium metal reacts with most common metals and refractories. Finely divided uranium reacts, even at room temperature, with all components of the atmosphere except the noble gases. The silvery luster of freshly cleaned uranium metal is rapidly converted first to a golden yellow, and then to a black oxide—nitride film within three to four days. Powdered uranium is usually pyrophoric, an important safety consideration in the machining of uranium parts. The corrosion characteristics of uranium have been discussed in detail (28). 

One-Step Cameras and Processors. The eadiest one-step cameras used roU film and completed processing inside a dark chamber within the camera (9). The first instant color film, Polacolor, was provided in roU film format to fit these cameras. Flat-pack film cameras (Fig. 2), introduced in 1963, permitted the film to be drawn between processing rollers and out of the camera before processing was completed (10). Film holders for instant 10 X 13 cm (4x5 in.) film packets contain retractable rollers that permit the film to be loaded without mpturing the pod (11). For 20 x 25 cm (8 x 10 in.) films, the processing rollers are part of a tabletop processor. The exposed film, contained in a protective black envelope, and a positive sheet with pod attached are inserted into separate slots of a tray that leads into the processor. The film passes through the rollers into a covered compartment within which processing is completed. 

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