The do's and don'ts of performing a macroetch is not something covered by the AWS CWI Seminar.
For the most part, you will be working with acids of various types that are diluted with water or alcohol. Any acid can be dangerous if not handled properly.
Number 1 - wear proper goggles to protect your eyes, better yet, a full face shield is better.
Number 2 - wear nital gloves to protect your hands from acid burns.
Number 3 - wear acid resistant lab jacket
Number 4 - be sure there is good ventilation. The fumes can damage the lining of the throat and lungs
Number 5 - make sure there is plenty of water at hand to flush any acid that comes in contact with your skin.
Procedure - grind and polish the specimen. I use a granite surface plate with plenty of emory paper of various grits. Start with course grit. Proceed to finer grit paper, but rotate the specimen 90 degrees each time you go to a finer grit. Remove all the scratches from the previous grit before moving on to the next finer grit.
The sample should be mirror smooth when you apply the acid. AWS B2.1 has some recommendations as to which etchant to use of different base metals.
Incomplete fusion, slag inclusions, etc. will be apparent by visual differences in the appearance of the discontinuity and surrounding base metal or weld metal. Typically, a crack, incomplete fusion, etc. will be darker than the surrounding metal. As mentioned, incomplete fusion on fusion face (fillet or groove weld) will appear as a dark straight line. Depth of fusion simply means the weld is fused to the fusion face. There is no requirement that it "measure" some minimal dimension. In some cases there is a need to minimize the depth of fusion to reduce the amount of dilution, but yet there must be evidence of fusion.
Etching samples is simply a matter of controlled corrosion. Certain metals or microstructures corrode or don't corrode as fast when exposed to various acids. The process should be performed only after receiving proper instruction form someone with experience handling acids and other hazardous liquids and gases.
ASM offers a class in the proper preparation and interpretation of macroetch samples.
I went to YouTube to see what was available on the subject. There were several videos avaialble. Like many videos, there are some that are by folks that are professionals, but there is still some useful information. One video demonstrated how oven cleaner can be used to etch aluminum, Naval Jelly can be used to etch carbon steels, etc. Here's a link to a video that illustrates some common weld defects.
https://www.youtube.com/watch?v=j7O7ysXpYTIGood luck.
Al