Glass fag here again. Id like to ad that you should slowly heat to 550 and slowly cool down from there.
If your using a flame to heat to 550 do not use a thin flame. You want it as big a flame as can be without rolling entirely over the sides. Also the lower the pressure to achieve that 550 the better.
Not all lab equipment is created equal and if youve got some thin ass garbage even the slightest bit of stress can fuck it up.
As always if youre unsure of your glass contact the manufacturer and save the emails so you can sue if youre injured by their product not meeting the standards they claim.
