In paintings, bloom is the result of a variety of causes. Sometimes it is due to moisture which deposits. At other times it is due to the action of sulphur gases on the chemical compounds in varnish; and one of the most general causes is a surface deposit to which dust and foreign matter adheres. Some varnishes, like Mastic, bloom notoriously; and, if Mastic is to be used, it always should be mixed with ten per cent. of Spike Oil and five per cent. of heavy-bodied Linseed Oil. This, in a large measure, prevents the flatting and blooming of Mastic Varnish.
Damar Varnish, at times, shows the same defect, but not to such a great extent as Mastic, and Sandarac, the latter being an alcohol soluble varnish, which shows it least of all, has the defect of cracking very readily, particularly a year after it is applied.
Bloom can be removed in many ways: First, by gently rubbing with a silk handkerchief, which removes the surface deposit and polishes the underlying film of varnish; second, by taking heavy bodied Linseed Oil, diluting with half Turpentine, and applying that with gentle rubbing, which at once polishes the surface and removes superficial adherent bodies; third, by the use of any good, thin machine oil, such as is sold in this country under the name of “3 In 1.” A few drops of this may be applied on a linen handkerchief and gently rubbed, but then it must be wiped completely clean, because it is a non-drying oil, and dust and dirt stick to it with greater ease than they do to a drying oil.
Bloom also occurs in damp atmospheres, even on a painting which is not varnished. This is due to a certain physical—chemical cause, in which even dried Linseed Oil will absorb a certain amount of moisture. To overcome this, the painting should be placed in the warm sun, wiped clean, and then revarnished with a very thin varnish of either Mastic or Damar.
REPAINTING
MANY painters and restorers are uncertain as to what materials to use for retouching and repainting. Some use Tempera colors; and, after they are dry, they varnish the entire picture, and the results are usually very good. With this exception, the Tempera colors do not change, whereas the surrounding oil painting yellows and darkens in undue proportion to the new color applied.
The best method to pursue is to use dry pigments, which should be rubbed, or mulled on a glass plate with a muller, and mixed with dilute Damar Varnish. The chances are that a mixture of this type will dry in fifteen or twenty minutes, and the color can be matched up with the surrounding painting very exactly. In filling up cracks, flakes and holes in paintings, this method is really the best, because it insures matching, quick drying and very little decomposition.
RESTORATION AND CLEANING OF PAINTINGS
THE greatest possible care in the selection of a cleansing material must be exercised, and it is always wise to take the painting out of the frame and try the effects of various mediums in one corner, in order to determine whether it is safe to clean the painting or not.
The first requisite is to wipe off the painting with a rag that has been soaked in boiling water and then wrung out, in order to remove superficial adherent dust and dirt. If the painting is cracked, it is necessary to be exceedingly careful not to let any moisture get through the cracks, for it might soften up the glue underneath, in which case, large flakes may possibly curl from the canvas. After having cleansed the surface with water or, if necessary, with any good neutral soap water, such as Ivory Soap, Fairy Soap; or, better still, any shaving soap, an experiment should be made in a corner of the painting, to see if it has been executed with a drying oil, like Linseed Oil, or Poppy Oil.