AUTOCHROME DIFFICULTIES. Green spots in the finished plate. These are caused through water penetrating the waterproof coating on the surface of the starch grains owing to its perforation, usually by particles of dust or rubbing in the plate holder. Mr. Essenhigh Cooke recommends cutting out the defect with a sharp knife and then filling in the blank clear glass with Chinese white tinted with colour to match the surrounding objects.

Bluish or too dark results. These are due to under-exposure.

Pinkish and too light results are due to over-exposure or overdevelopment in the first solution. To get the true effect of a lady in a white dress or a sunlit snow scene it is often necessary to develop only for 30 seconds or 1 minute. The whole of the silver must not be reduced when developing the first or negative image, for in this case the permanganate bath leaves nothing for the second development.

Some Supplementary Suggestions, etc., by Messrs. Lumiere.

DEVELOPMENT (CONCENTRATED QUINOMET) (a).

Water ............

1000 c.c. or 35 ozs.

Quinomet (b)..........

15 grammes or 1/2 oz.

Anhydrous sodium sulphite

100 grammes or 3 1/2 ozs.

* Ammonia .920 (22o Baume)

32 c.c. or 9 drams.

Potassium bromide ......

6 grammes or 90 grains.

Bath C. Reversal.

1000 c.c. or 35 ozs.

Potassium permanganate

2 grammes or 30 grains.

Sulphuric acid ........

10 c.c. or 3 drams.

(a) This concentrated developer may be purchased in bottles of 17 ozs., 9 ozs., 4 1/2 ozs. For use it is diluted with four times the quantity of water (1 oz. concentrated solution to 4 ozs. water).

(b) The Quinomet should be dissolved in warm water (about 100°), the sulphite added and then the ammonia.

* Ammonia .920 may be prepared by adding 1 oz. of water to 2 ozs. ammonia .880, the strength which is usually sold in Great Britain.

METHOD OF FIRST DEVELOPMENT

In cases of uncertain exposure.

The automatic development for a fixed time (2 1/2- minutes) is applicable only when exposure is known to be practically correct ; if it be used invariably, regardless of exposure, the resulting image is liable to be thin and without detail, in the case of over-exposure, or dense and insufficiently developed in the case of under-exposure.

We have, therefore, devised the following method, which, while less simple than the former, indicates (according to the time elapsing between immersion of the plate in the developer and appearance of outlines of image), the length of development necessary to obtain a good result.

The dark-room lamp should be fitted with Lumiere " Virida " papers..

FOR THE DEVELOPMENT OF ONE HALF-PLATE.

(1) Put in one measure glass 15 c.c. (1/2- oz.) and in another 45 c.c. (1 1/2- ozs.) of the concentrated quinomet developer.

(2) Put in the developing dish

How To Secure Instantaneous Exposures On Autochrom 54

Immerse the plate in this solution and count the number of seconds elapsing before the first outlines of the image appear, disregarding the sky. Immediately the outlines are discernible, pour into the dish either 15 c.c. (1/2 oz.) or 45 c.c. (1 1/2 ozs.), whichever may be necessary according to the following table, continuing to count the seconds : -

Appearance of outlines of image (disregarding sky) after immersion.

Quantity of developer to add on appearance of first outlines.

Total duration of development (immersion of plate).

Seconds.

12 to 14

15 " 17

18 " 21 22 " 27

28 " 33 34 " 39

15 C.C. ( 1/2 OZ.) do. do. do. do. do. do. do. do. do. do.

Minutes.

1 1 2

3 3 4

Seconds.

14 45 15

30 30

Extreme underexposure.

40 to 47 Above 47

45 C.C. (1 1/2 ozs.) 45 c.c. (1 1/2 ozs.)

3 4

For a plate 4 1/4 X 3 1/4 use half the above quantities. The succeeding operations : reversal, second development, and, if necessary, intensification, proceed as usual.

The makers supply the above table printed on transparent paper. For reference during development it may be affixed to the window of the lamp.