b. The dried coating thickness of wet suspended developer is critical. If the coating thickness is excessive,
the layer can reduce or mask the visibility of flaw indications. The thickness of the dried developer
layer depends upon the concentration of developer in the water. Figure 2-24 shows the results of having
optimum versus excessive thickness of developer layer on a cracked aluminum panel.
c. The liquid developer is mobile on the part surface before drying, and it may flow into and collect in
cavities or recesses, leaving an excess of developer. This local build-up can be reduced by careful
handling and positioning of the part.
d. Even though the water suspendible developers contain a biocide, eventually bacterial growth will occur.
Bacterial growth is evidenced by foul odors, discoloration and/or foreign material in the suspension.
Once bacterial growth is noticed the suspension must be discarded and the tank completely disinfected
before mixing a new suspension.
Figure 2-24. Cracked Aluminum Panel Comparing Results with an Optimum Thickness Layer (Top) to an
Excessive Layer (Bottom) of Developer.
Water Soluble Developer.
Water soluble developers contain developer particles, wetting agents, corrosion inhibitors and biocides. They differ
from wet suspended developer since the particles dissolve in water to form a clear, lightly tinted solution. During the
drying process, the developer particles crystallize out of solution as the water evaporates. The resultant coating is a
thick, readily visible white. The dry layer is thicker than wet suspended developer coating, and much thicker than a dry
Wet, soluble developers are supplied as dry powders and must be dissolved in water before use. The proportions of dry
powder to water depend upon the type of developer and the manufacturer. The manufacturers recommendations on
concentration SHALL be followed. In making up the bath, the dry powder must be stirred into the water until it has
completely dissolved. Since the developer particles are dissolved in the solution, agitation is not required after the
developer has been initially mixed with water.