sodium persulfate microwave heating cause crystallized particles
It looks to me like copper sulphate ($\ce{CuSO4·nH2O}$). If I'm right then you can't use it for etching. For this you need oxidant (persulphate). Try to solve this solid in water. You should get light blue solution. Stick into it a nail (i.e some metal iron source). If it cover itself with a brownish powder like in wiki-link you gave, then it's a copper(+2) salt.