Glass roll, glass roll manufacturing method, and quality evaluation method

A glass roll manufacturing method comprising:

• a forming step of cooling and solidifying a glass ribbon, which is obtained by forming molten glass into a band shape with a forming trough, while pulling the glass ribbon in a longitudinal direction, to thereby obtain a band-shaped glass film having creases formed thereon, the creases forming an unevenness of a surface of the band-shaped glass film without cracks, and the creases not being eliminated with an application of tension to the band-shaped glass film;
• a dividing step of dividing unnecessary portions that are respectively present at both ends in a width direction of the band-shaped glass film from an effective portion positioned between both the unnecessary portions;
• a winding step of winding up the effective portion of the band-shaped glass film into a roll shape, to thereby obtain a glass roll;
• and
• a measurement step of measuring a length of a section of the effective portion from a leading end portion of the section to a trailing end portion of the section along a surface of the section at each of one side end portion and another side end portion in a width direction of the effective portion, the leading end portion and the trailing end portion of the section extending parallel to the width direction of the band-shaped glass film,
• wherein, when a difference between a first measurement length and a second measurement length which are respectively measured along the one side end portion and the another side end portion is more than 400 ppm of a longer measurement length of the first measurement length and the second measurement length, a first adjusting step of adjusting to reduce the difference between the first measurement length and the second measurement length is performed.