This is a 75% hydration sourdough, with 3-4 hour initial fermentation and finished ~12 hours in a fridge. Then it was shaped, slashed with the long edge of a kitchen knife (at a ~30' angle) and placed into a 475' oven. I did not use a cover or a crock pot to bake.
The problem I have is that my slashes always seem to close up, often opening at the bottom. If you look at this picture closely, you can see that there are remnants of slashes on the top of the bread (aside from the humps) - those slashes are from me slashing the bread again ~5 minutes after the bread went into the oven.I have never been able to get good scores and they always seem to close up.
What am I doing wrong and what can I do to correct these problems?