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Home >>Professional Decorating>>Decorating Museum>>Loss of Gloss
Decorating Defects - their cause and cure
Loss of Gloss
To a large extent, the degree of gloss which a paint or enamel film exhibits depends on the proportions of oil or resins to pigment used in formulating the paint. If the volume of linoxyn (i.e. linseed oil which has dried to a tough film) is greatly in excess of the volume of pigment, the particles of the latter are submerged in the vehicle, which coats and binds them together and fills in and bridges the minute gaps between them, producing a smooth and lustrous film.
When, on the other hand, there is only a small proportion of vehicle to pigment, the particles protrude through the surface of the film. As their planes are set at widely different angles, light striking a surface of this kind is broken up and reflected in many directions, thus producing what is known
as a flat finish.
At the same time, the type and characteristics of the pigment may have a definite effect on the degree of gloss. Fineness of grinding, for instance, is an important factor and this explains why the high-grade factory-made
finish has such good gloss. In coarsely ground paints, the irregularity of the pigment particles breaks up the continuity of the film and thus detracts from the gloss.
The opacity of the pigment must also be taken into consideration. Some, as for example, Prussian blue or pure Indian red, have great opacity and this enables a less amount of pigment to be employed than when other pigments which have poor obscuring properties are employed. Again, certain pigments, such as chrome yellow or Indian red, tend to sink and lie within the film, so that a minute skin of almost clear vehicle seems to float to the top.
All paints, enamels, and varnishes gradually lose their gloss after having been exposed for some time, though the efficiency of their film as a protective agent is not necessarily impaired thereby. Atmospheric deposits and influences slowly act upon and wear away the linoxyn, or oxidised linseed oil, exposing the pigment particles and breaking up the lustrous surface; one method of preserving gloss, therefore, is to keep the surface clean, water and a polishing leather being as effective as anything for this purpose.
It should be remembered, however, that the repeated use of strong alkaline solutions by housewives in maintenance cleaning will tend in time to destroy the binder of the paint and thereby cause loss of gloss. Again, the employment of many of the various brands of household scouring powders (which, though they are advertised as being suitable for cleaning paintwork, contain far too much gritty or abrasive matter for the purpose) will have a similar effect.
Loss of gloss, however, occasionally occurs in a painted or enamelled surface too soon after the finish has been applied. The most likely reason is that the ground on which it has been put on is too porous, with the result that a proportion of the vehicle is filtered off by absorption, leaving an over-pigmented and consequently a flat or semi-flat film. Care should be taken, therefore, that the last coat is not too flat and under-bound, or it may tend to rob the finishing coat of its vehicle.