Hi Mustafa Have a look here
Home › Forums › Glass Fusing › General Fusing Discussion › Optical Glass Clay and is it similar to bronze clay › Hi Mustafa Have a look here
Have a look here for views of the product “GlasClay” … http://www.delphiglass.com/fusing-sale/fusing-kits-sale/glasclay-kit-96-coe and note that there is a book available on the topic which may be worth reading before you commit to spending toomuch money : http://www.delphiglass.com/books-dvds-software/fusing-books/glasclay-basics .
And, as Barry states, it is opaque by the look of the examples.
Good luck and enjoy creating