Caramel . . . . . . . . . 2 oz.

Gum solution . . . . . . . 1 ,,

Burnt Sienna . . . . . . . 1 to 2 oz.

Methylated Spirit . . . . . . . 2 oz.

A little golden syrup is occasionally added. Grind together sienna and caramel in a mortar, add the other ingredients, and apply to back of plate with a flat hog-hair brush. Flexible backing pads will not often adhere uniformly, and therefore are not an efficient substitute for the soluble backing.

Stoppered Glass Bottles, To Ease

The stoppers may generally be loosened by one or other of the following expedients, according to the cause which has rendered them immovable: (1) Let a drop of sweet oil or warm water fall on the line formed by the junction of the stopper with the neck of the bottle. (2) Apply warm water or heat . in some way to the neck of the bottle. (3) Tap the stopper smartly all round with a piece of wood.

Prints: Finishing Off

When prints are taken from the final washing water they may be surface-dried with clean, hard blotting paper, and hung up to dry, or squeegeed on pulp slabs to give them a glossy appearance. Prints should never be cut with scissors, but trimmed with a sharp knife against a glass-cutting slab, to ensure integrity of line.

Mountants For Prints

(1) Gulliver's Paste is probably the very best for ordinary use. It keeps well, and prints do not cockle.

Picked White Gum Arabic..... 1/2 oz.

Dextrine . . . . . . . 2 1/4 ,,

Ammonia ........ 4 drops.

Carbolic Acid . . . . . . 1 dr.

Water........ 8 oz.

The gum arabic is pounded in a mortar, and mixed well with the dextrine; then triturate with 2 oz. of water till quite smooth, when the rest of the water is added, and the whole boiled for 10 minutes. When nearly cool, add ammonia and carbolic acid, and bottle off.

(2) A gelatine mountant which forms a strongly adhesive liquid may be prepared by dissolving ordinary flake or sheet gelatine in a 15 per cent. solution of barium chloride. The latter is then precipitated by the addition of sodium sulphate, when barium sulphate is left as a white deposit, and the clear liquid may be poured off.

(3) Gelatine......... 3 oz.

Water . . . . . . . . . 20 ,,

Glycerine . . . . . . 2 „

Methylated Spirit . . . . . . 10 „

Soak the gelatine till soft, when apply heat sufficient to melt it, and add the other ingredients, stirring rapidly. When using, place the bottle containing the mountant in warm water.

(4) Dextrine Mountant : Mix a pound of best white dextrine into a stiff, even paste with cold water; then add 1/2 pint of warm water and 1 dram oil of wintergreen; bring the mixture to the boil, and decant into pots. It will be ready for use in about 12 hours, and will keep for some months.

Encaustic Paste

A preparation to be rubbed on the finished and mounted print as a preservative, and also to give a glossy surface. Polish on with a piece of cottonwool or soft silk handkerchief. Dr, Eder's prescription is:

Pure White Wax...... 100 gr.

Oil of Turpentine . . . . . . 100 min.

Gum Dammar Varnish . . . . . 40 ,,

Burnishing

A method of finishing prints not at present in great favour. The prints are first prepared by being rubbed over with a lubricator, consisting of 15 gr. castile soap in 2 oz. methylated spirit, applied with a soft flannel. When dry they are drawn steadily through the burnisher, the iron of which must be clean and free from scratches, and just hot enough for the hand to bear comfortably. Uniform motion is the great secret of success in burnishing; marks and scratches are produced by stoppages or jerky movements.

Glass, To Clean

Powdered Chalk....... 2 oz.

Ammonia ........ 1/2 „

Water......... 1 1/2 „ is as good a mixture as any, 1 oz. fine pumice powder being sometimes added. Rub on with a piece of wash-leather, and finish with soft rag or paper.

Baryta Paper

A hard-surfaced paper, used as a support for gelatine printing-out emulsions and in collotype. The formula generally given is:

A. Gelatine (Heinrich's) . . . . . . 90 gr.

Barium Chloride . . . . . . . 30 ,,

Distilled Water . . . . . . 5 oz.

B. Ammonium Sulphate . . . . . 15 gr. Distilled Water....... 2 1/2 oz.

Soak the gelatine, and dissolve by heat, adding the barium; then add solution B by degrees, shaking between each addition. Allow emulsion to set; break into small pieces, and wash thoroughly. Lastly, add about 7 1/2 gr. chrome alum, dissolved in a little water.

Silvering Mirrors

A. Silver Nitrate....... 175 gr.

Distilled Water...... 10 oz.

B. Ammonium Nitrate ..... 262 gr. Distilled Water . . . . . 10 oz.

C. Pure Caustic Potash . . . . . 1 „ (437 1/2 gr.) Distilled Water . . . 10 „

D. Pure Candied Sugar . . . . . 1/2 „ Distilled Water...... 5 „

Dissolve the sugar-candy in the water, and add 50 gr. tartaric acid. Boil for a few minutes, and, when cool, add alcohol 1 oz., and make up to 10 oz. with distilled water. For use, mix equal parts of A and B and equal parts of C and D in two separate flasks. Then mix the two in the silvering dish, and suspend the glass plate, which must be spotlessly clean and free from grease, face downwards.

British Weights And Measures. Avoirdupois Weight

437 1/2 grains = I ounce. 16 ounces = 1 pound = 7000 grains.

Fluid Measure

60 minims = 1 drachm. 8 drachms = 1 ounce. 20 ounces = 1 pint. 1 fluid ounce weighs 437 1/2 grains. 1 minim weighs 91 grains.

Conversion Of Metric Into British Weights And Measures. Grammes Into Grains And Ounces

Grammes.

Grains.

0.065

1

0.l

1.5

0.2

3.1

0.3

4.6

0.4

6.2

0.5

77

1

15.43

2

30.9

Grammes.

Grains.

3

46.3

4

61.7

5

77.2

10

154.4

14.17

1/2 oz.

21.26

3/4 oz.

28.35

I oz.

Cubic Centimetres Into Minims And Ounces

Cubic Centimetres.

Minims.

•06

1

.3

5

•6

10

.9

15

I

16.9

2

33.8

3

50.7

Cubic Centimetres.

Minims.

4

67.6

5

84.5

10

169

14.17

1/2 oz.

28.35

1 oz.

50

1 oz. 365 min.

100

3 oz. 250 min.

Millimetres To Inches

Millimetres.

Inches

I

•04

2

•08

5

•2

Millimetres.

Inches.

10

•39

20

79

25.4

1.0

Comparative Sizes Of English And Foreign Plates

Centimetres.

Inches.

English Quarter Plate

10.8 x 8.25

4 1/4 x 3 1/4

French „ „

9 X 12

4.72 x 3.54

English Half Plate .

16.5 X 12

61/2 x 4 3/4

French „ „

13 x 18

7 x 5.12

English Lantern Plate

8.25 square

3 1/2 in. square

French „ „ .

10 x 8

3.85 x 3.2

American „ „ .

10.16 x 8.25

4 x 3 1/4

Diaphragm Numbers. United States System Compared With Focal Equivalent System

The United States system corresponds with the relative exposure required.

Focal Number

4

5.6

8

11.3

16

22.6

32

45.2

United States Number

1

2

4

8

16

32

64

128

Thermometric Table

Centigrade.

Reaumur.

Fahrenheit.

100

80

212

Boiling point of water

95

76

203

90

72

I94

85

68

185

80

64

176

75

60

167

70

56

158

65

52

149

60

48

140

55

44

131

50

40

122

45

36

113

40

32

104

35

28

95

30

24

86

25

20

77

20

16

68

15

12

59

10

8

50

5

4

41

0

0

32

Freezing point of water

Table Of Distances For Enlargements

Focus of

Lens.

Times of Enlargement.

1

2

4

5

6

7

8

3

6

9

12

15

18

21

24

27.

3 1/2

7

10 1/2

14

17 1/2

21

24 1/2

28

31 1/2

4

8

12

16

20

24

28

32

36

4 1/2

9

13 1/2

18

22 1/2

27

31 1/2

36

40 1/2

5

10

15

20

25

30

35

40

45

5 1/2

11

16 1/2

22

27 1/2

33

38 1/2

44

49 1/2

6

12

18

24

30

36

42

48

54

7

14

21

28

35

42

49

56

6.3

8

16

24

32

40

48

56

64

72

The figures in the above table give the distance required between centre of lens and sensitive surface; to find distance between lens and transparency divide the figure given by the number of times. Thus with a 3-in. lens for same size, distance between negative and centre of lens must be 6 in., for double size 4 1/2 in., for three times 4 in., etc., etc. Directions for ascertaining focal length are given on page 38. These figures reversed will serve also for reductions.

Table Of Comparative Speed Numbers Of Plates

Hurter and Driffield.

Watkins.

Wynne.

10

15

24

20

30

28

40

60

49

80

120

69

IOO

147

77

140

206

91

200

294

109

300

441

134

400

588

154