The characteristics of a good blackboard surface are intense black and absence of gloss; the former is desirable, inasmuch as the greater the contrast between the chalk marks and the colour of the board the more clearly will the characters show up. But that all gloss should be absent is more important still, as unless the lighting of the room is very favourable, a board having a glossy surface is sure to cause annoyance and trouble. A glossy board reflects the light, and, in consequence of this, it will be found that from some part of the room, at any rate, chalk marks on the board cannot be seen clearly. Therefore, the aim in blackening a board must be the production of a surface containing as little gloss as possible. There is no best way of blackening a board, as all dressings will, sooner or later, become polished by the constant friction of chalk and duster; and, in a general way, coatings that are less liable to this polishing action have another drawback. This is the difficulty of rubbing out the chalk marks that to some extent is possessed by all coatings in the composition of which an abrasive material, such as emery or pumice powder, enters, and which contain little or no binding agent in the form of shellac or gum.

The following recipes and instructions are given as the result of much experimenting on the part of those who have afterwards published the results, and it is believed that below will be found almost every recipe of importance that has been made known during the last twenty years. The compositions given in recipes Nos. 1 to 7 are all applied over two, or preferably three, good coats of colour made with whits lead, boiled oil, black pigment, and turpentine. Glasspaper each coat, which should be quite dry before the next is applied. Of course, the board should previously have been planed or glasspapered smooth.

(1) (live a coat of Hat drop black and japan gold size containing 1/2 lb. of flour emery to 1 pt. of black pigment. When dry, coat again; but add 1 part of turps to 3 parts of gold size used in the former coat.

(2) Coat thinly but evenly with common black and driers and 2 parts of linseed oil to 1 part of turpentine. When dry, spread quickly a mixture of 3 parts (by measure) of best ivory black ground in turps and 1 part of japan gold size, and dilute with turpentine.

(3) Give two coats of black mixed with boiled oil; smooth, when dry, with flour emery paper, then coat with black mixed merely with turpentine.

(4) Coat with common dark lead colour or with common black paint, and then with a mixture of ivory drop black ground in turps, copal, or carriage oil varnish and turpentine. The greater the quantity of varnish used the greater will be the gloss; but some varnish is necessary to bind the colour.

(5) Apply japan black and stipple a finish flat.

(6) Give two coats of paint containing an excess of driers. Glasspaper the board after the first coat.

(7) Give two coats of varnish colour, containing just enough varnish to produce an "egg-shell" gloss. When thoroughly hard, rub dowu with felt and pumice powder, and leave for a few hours before using.

(8) The new board is well sized and then coated twice with oily, dark lead colour or common black paint. Before twenty-four hours have elapsed, apply a mixture of ivory drop black ground in turps, japan gold size or copal varnish, and enough turps to give a thin, watery consistency. This should produce a flat and lustreless black surface.

(9) Grind lampblack in spirit varnish or alcohol, add sufficient flour emery to give a suitable surface, and thin with spirit varnish. Apply to the smooth board with a paint brush; allow to become thoroughly dry and hard, and rub down with pumice if too rough.

(10) Dissolve in 4pt. of alcohol (95 per ceut.) 8oz. shellac, and add lampblack 12dr., ultramarine blue 20dr., powdered rottenstoneloz., and powdered pumice-stone 6 oz. Shake the preparation and apply it with a new flat varnish brush as quickly as possible to the board, which must be free from grease. Keep the bottle well corked. Instead of alcohol, the shellac may be dissolved in a solution of borax in water, and coloured with lampblack.

(11) Dilute silicate of soda (water glass) with an equal bulk of water, and add sufficient lampblack to colour it. Before being added, the lampblack should be ground with water and a little of the silicate.

(12) Give the new board two coats of lampblack mixed with boiled oil and patent driers, and, when quite dry, coat with a mixture of burnt lampblack and turpentine. To prepare this mixture, place i lb. lampblack on a flat piece of tin or iron on a fire till it becomes red; take it off and leave it until sufficiently cool, when it must be crushed with the blade of a knife on a flat board quite fine; then mix with 1/2 pt. of spirit of turpentine, and apply with a size brush.

(13) One gallon of blackboard dressing may be made by rubbing into a thick paste 10 oz. of powdered pumice-stone, Ooz. of powdered rottenstone (or infusorial silica), 12 oz. of lampblack, and sufficient methylated spirit. Mix this with the remainder of a gallon of spirit in which 14 oz. of shellac have been dissolved. Apply two coats, constantly stirring the paint. Apply the second coat lightly. This quantity of dressing is sufficient for 60 sq. yd. of board.

(14) First coat with a mixture of shellac varnish and lampblack, and when dry, with three coats of a mixture of 1/2 gal. shellac varnish, 5 oz. lampblack, and 3 oz. powdered iron ore or emery; if too thick, thin with alcohol. Allow each coat to dry before putting on the next.

(15) Give two or three coats of a solution of 10 parts of shellac in 90 parts of alcohol to which has been added 1 part of lampblack, 1 1/2 parts of ultramarine, 5 parts of powdered Rochelle salt, and 7 parts of powdered pumice-stone.

(16) Apply a dressing made by dissolving 20 parts of shellac in 200 parts of alcohol aud adding 10 parts of ivory black, 6 parts of flour emery, and 5 parts of ultramarine.

(17) Grind equal quantities of dry red lead and pumice powder in good varnish thinned with turps; add sufficient lampblack, and thin with turps. If desired, substitute wood naphtha for the alcohol and gold size for the varnish.

(18) A good imitation slat inn-is produced by applying pulverised slate or quartz rock, using silicate of soda (water glass) as the medium.

(19) Give two or three coats of asphaltum dissolved in petroleum naphtha.

(20) In many schools the walls are made to serve the purpose of blackboards. The walls are first coated with a size made by dissolving lib. of glue in lgal. of water and adding a little lampblack. When dry, apply one of the above dressings.

(21) Most of the compositions mentioned above are of the nature of paints, but stains are sometimes employed for the purpose, and meet with partial success. Throe methods of staining boards are here given. Break loz. of nutgalls into small pieces and steep for half an hour in 1/2pt. of vinegar contained in an open vessel. Add loz. of steel filings, allow to stand untouched for two and a half hours, and then apply it with a brush. The second method is to brush in a solution of sulphate of iron, which should be allowed to soak into the wood, and then to sponge with a solution of nutgalls until sufficiently black. The third method is to apply a boiling solution of 1/2lb. of logwood in water; this should have stood for twenty-four hours and should then have been strained. When dry, give another coat, and when this is dry well rub the surface of the board with straw or something similar, and then apply one or two coats of a boiling solution of 4 oz. of copperas in 1 pt. of water. Chalk marks are not easily rubbed out on this at first, but the difficulty is lessened in a few days. The above instructions are on treating new boards, but recipes Nos. 9 to 20 are also suitable for renovating old surfaces.

If for this purpose recipes Nos. 1-7 are also employed, proceed as if treating a new board which has already received its preparatory coats of oil paint. It may be mentioned that at many schools blackboards are successfully re-blackened by a weekly or bi-weekly application of ordinary black writing ink.