ron lake - soldering

[john april]

i bought the 'how to make folding knives' book by ron lake,frank centofante and wayne clay. in ron's section of the book is this photo of an an air fitting. he mentions silver solder, so i assume he means the hard high temp solder. are pin holes actually the impurities the flux has cleaned off which has risen to the top of the joint , like slag floats on top of molten metal? would this also work for lower temp silver bearing solders like sta-brite ? there is no mention of how it is used in the book, just the photo. how would it be used ? heat the joint, blast it out with air, reheat and apply solder? re- flux after the air? thanks for any info.