Some examples of possible breaker contact surface conditions  are illustrated in  Figure 4-62 . Item A illustrates an example  of erosion or wear called frosting. This condition results from  an open-circuited condenser and is easily recognized by the  coarse, crystalline surface and the black “sooty” appearance  of the sides of the points. The lack of effective condenser  action results in an arc of intense heat being formed each  time the points open. This, together with the oxygen in the  air, rapidly oxidizes and erodes the platinum surface of the  points, producing the coarse, crystalline, or frosted appearance.  Properly operating points have a fine-grained, frosted, or  silvery appearance and should not be confused with the coarse- grained and sooty point caused by faulty condenser action. However, when wear advances to a point where the slight,  smooth irregularities develop into well-defined peaks  extending noticeably above the surrounding surface, the  breaker contacts must be replaced.  [Figure 4-61] Unfortunately, when a peak forms on one contact, the mating  contact has a corresponding pit or hole. This pit is more  troublesome than the peak because it penetrates the platinum  pad of the contact surface. It is sometimes difficult to judge  whether a contact surface is pitted deeply enough to require  replacement because this depends on how much of the  original platinum is left on the contact surface. The danger  arises from the possibility that the platinum pad may already  be thin as a result of long service life and previous dressings. Figure 4-62B  and  C  illustrate badly pitted points. In the early  stage, these points are identified by a fairly even contact edge  and minute pits or pocks in or near the center of the contact  surface with an overall smoky appearance. In more advanced  stages, the pit may develop into a large, jagged crater, and  eventually the entire contact surface takes on a burned, black,  and crumpled appearance. Pitted points, as a general rule,  are caused by dirt and impurities on the contact surfaces. If  points are excessively pitted, a new breaker assembly must  be installed. At overhaul facilities, a gauge is used to measure the  remaining thickness of the pad, and no difficulty in  determining the condition of the pad exists. But at line  maintenance activities, this gauge is generally unavailable.  Therefore, if the peak is quite high or the pit quite deep,  remove and replace them with a new assembly. A comparison  between  Figures 4-60  and  4-61  will help to draw the line  between minor irregularities and well-defined peaks. wear and are not cause for replacement. Figure 4-62E  illustrates a built-up point that can be  recognized by the mound of metal that has been transferred  from one point to another. Buildup, like the other conditions  mentioned, results primarily from the transfer of contact  material by means of the arc as the points separate. But, unlike  the others, there is no burning or oxidation in the process  because of the closeness of the pit of one point and the buildup  of the other. This condition may result from excessive breaker  point spring tension that retards the opening of the points or  4-37 Figure 4-62.  Examples of contact surface conditions. Figure 4-61.  Points with well-defined peaks. Figure 4-60.  Points with normal irregularities.  A B C D E F