We are placing sienna earths in the group of brown pigments for the reason that they really differ vastly from yellow ochers in both tone, strength and chemical constituents, at least so far as the percentages of the latter are concerned.

Sienna earth, or natural sienna, so called after a town in Italy, not very far from Rome in the hills, where underneath the top layers of earth over the rocks the material was at one time found in abundance, is a yellow pigment with a more or less brownish red tinge in the solid and a more or less yellowish undertone. It differs from the best French yellow ocher by having a much deeper color, more than twice the tinting power, containing only two-fifths as much silica, only one-third as much alumina and from two and one-half to three times as much ferric oxide, and in addition to this from one to one and one-half per cent of manganese oxide, to the presence of which is due the difference in color. The localities where sienna earth is found are not confined to the original one near the town of Siena, but all through Tuscany and in the Hartz Mountains of Germany, earth of similar quality is found. In the United States in Pennsylvania deposits of sienna earths are found, and in the mountain ranges of Virginia good, rich deposits have been developed. The present commercial offerings to the trade vary from very strong decided yellow toned earths to those of a decidedly russet tone. Up to twenty years ago no painter would have purchased the yellow raw siennas that are great favorites with some painters to-day, because of the strong yellow tints produced with white, thereby displacing yellow ochers to quite an extent. The raw sienna in oil on the market up to that time was the kind that when ground fine in oil showed up with excellent transparency and when used for staining white lead made an excellent oak graining ground without any other addition. A certain old-established firm of oxide and color makers discovered a mine of earth in Virginia, which they developed and found to be very high in oxide of iron with all the other constituents of sienna in combination. At that time the movement for pure oil colors of exceptional strength was at its height and the firm in question floated, dried and powdered part of the earth, while they calcined another part, thus obtaining very strong raw and burnt sienna that when ground fine in oil, put all the Italian sienna in the shade for tinting power, because while the latter required more than its own weight of oil for grinding, these new products only required 40 per cent of oil for the raw and 35 per cent for the burnt. The concern in question, by diligent advertising among color grinders, sold so much of the product that the best veins in the mines were exhausted in a very few years, and later mining did not produce the strong products. Still it was the start among the consumers of oil colors to favor the raw sienna, producing the yellow tint with white. Ordinary domestic siennas, that grind well in 35 per cent oil to 65 per cent of pigment and resemble the tone of the old-fashioned Italian goods, are rather dull, somewhat gritty and lack tinting power. The following will give a good idea of an average Italian raw sienna of fair quality in comparison with average domestic product: -

Italian Sienna, Raw

Per cent

Combind water (H2O) ...............................................................

9.67

Ferric oxide (Fe2O3) ..................................................................

53.83

Alumina (Al2O3) .......................................................................

5.85

Silica (SiO2) ..............................................................................

28.25

Calcium carbonate (CaCO3) .....................................................

1.12

Manganese (MnO2) ..................................................................

1.28

Total ...................................................................................

100.00

American Sienna, Raw

Per cent

Combined water (H2O) .............................................................

10.24

Ferric oxide (Fe2O3) ..................................................................

32.13

Alumina (Al2O3) .......................................................................

15.60

Silica (SiO2) ..............................................................................

38.10

Calcium carbonate (CaCO3) .....................................................

2.17

Mamganese (MnO2) .................................................................

1.76

Total ................................................................................

100.00

All the hygroscopic moisture had been removed before the analyses were made. The siennas of which analysis is shown here required 52 per cent raw oil to 48 per cent pigment by weight for the Italian and 36 per cent raw oil to 64 per cent pigment in the case of the American for mixing and grinding, producing a good buttery paste in each case.

Discriminating painters will not take kindly to the native sienna, unless it is of the exceptional strength referred to above, and even then they will prefer the old fashioned Italian material, when it comes to graining in oil or distemper, where the tone is of importance. The same applies when it comes to a selection of raw sienna for artists' tube color, while for grinding in japan the softer Italian grades are also preferred. Artists will prefer the browner surface tone in raw sienna and the nearer it comes in its general tone and the tint produced in admixture with white to the raw or natural sienna offered by Winsor and Newton, the better it is liked by them. Raw Italian sienna of that grade requires more than its own weight of oil for mixing and grinding, and will run about 40 of pigment to 60 of oil by weight. Car painters, who use raw sienna in japan for graining purposes on quick jobs also prefer this type, as it works more easily and is not so apt to sag or run, as those that carry an extra high percentage of oxide of iron. It seems rather queer, but is an established fact, that yellow ochers and siennas, that show exceptionally high percentages of iron oxide do not work as well under the brush as those of a lower percentage. Presumably this is due to a lack in the portion of gangue required to give the characteristic properties desirable in each. While in a mixed paint, such voids can be filled, it is not feasible to effect this in an oil color for several reasons. First of all, any experienced analyst would discover the deception and brand it as an adulteration, and secondly the addition so made would not produce the effect as completely as is done by nature. Raw sienna is, as noted above, used as a water color, ground to a fine paste without size, by grainers and in distemper work, and 50 pounds pigment mixed with 60 to 65 pounds of water will produce 100 pounds of finished paste. It is put up like all distemper colors, preferably in well sealed glass jars, because otherwise it will soon become dry and hard, on account of the evaporation of the water.