GB585279A - Improvements in or relating to photographic development processes - Google Patents

Abstract

585,279. Photographic development. TULL, A. G. Feb. 13, 1945, No. 3543. [Class 98 (ii)] The sulphite is removed from an aqueous colour or tanning developing solution before any substantial development or colour formation has begun and without oxidation of the developer, e.g. by the addition of an oxidizing agent such as bromine, sodium hypochlorite, potassium ferricyanide, ferric chloride, ceric sulphate, or alkaline hydrogen peroxide ; by the addition of a water-soluble alkaline earth compound such as barium chloride ; or by the addition of an aldehyde or ketone. The process may be applied to a colour developing bath containing a diamine or an aminophenol as a developing agent or to a tanning developer containing pyrogallol, pyrocatechol, or hydroquinone as a developing agent. The sulphite may be a neutral sulphite, bisulphite, or metabisulphite. The photographic material may be treated in a barium chloride bath prior to development. In a two-bath process, the first bath may comprise the developing agent and sulphite and the second bath the coupler, the alkali, and the sulphite-precipitant, or in the case of a direct colour developer or a tanning developer the alkali and the sulphiteprecipitant. Barium hydroxide may be used both as alkali and sulphite - precipitant. Galcium or strontium hydroxide may be used in conjunction with a more soluble alkali (such as sodium, potassium, or ammonium hydroxide, a tribasic alkali phosphate, a borate, or an organic amine), the former being maintained in excess by the suspension' of blocks in the developing bath. The solutions may be buffered to a definite pH. The material may be treated with an oxidizing agent before or after application of the developer. If acetone is added as sulphite precipitant, no other alkali is needed. A deposit on the photographic material may be removed in a dilute acetic acid bath. In example 1, a comparison is made between the colour developing action of a developer containing 2-amino-5-diethylaminotoluene hydrochloride, sodium sulphite, potassium bromide, barium chloride, ammonium hydroxide, 2 : 4 - dichloro - 1 - naphthol and alcohol, and the same developer without barium chloride. In example 2, sodium. peroxide, hydrochloric acid, sodium carbonate and alcoholic 2 : 4-dichloro-1-naphthol are successively added to a developer containing 2-amino- 5-diethylaminotoluene hydrochloride, sodium sulphite and potassium bromide. Hydrogen peroxide may replace the sodium peroxide. In example 3, a bleached silver salt image is redeveloped in a bath containing 2-amino-5- diethylaminotoluene hydrochloride, sodium sulphite and potassium bromide 'and is then treated in'a bath containing barium hydroxide, borax and alcoholic coupler. In example 4, a film carrying an unhardened gelatino silver salt emulsion containing Tartrazine is exposed through the support with blue light to a negative image, is developed in a bath comprising pyrogallol, potassium bromide, ammonium chloride, sodium sulphite and sodium hydroxide and is then washed out in hot water to give little or no relief image. By addition of calcium chloride to the developer, a relief image is obtained. Specification 580,496 is referred to.