Fixing bent corners on baseball cards requires carefully straightening them without causing further damage. The steps involve softening the card stock with moisture to make it pliable again without weakening it, gently pressing the corners flat, and allowing them to dry flat over multiple days.

The first step is to humidify the card to soften the paper fibers without over-saturating the stock. Carefully mist the corner of the card lightly with a spray bottle of distilled water, applying very little at a time. You want the paper to become slightly flexible but not soaked through. Leave it to absorb the moisture for 5-10 minutes.

Care must be taken not to apply too much moisture at once as it could cause streaking, warping or weakening of the paper. Build it up gradually and check the flexibility often by gently trying to flatten the bend with your finger. You want it supple enough to reshape but not so wet that it loses its form when handled.

Once lightly humidified, use a soft flat tool like a credit card or ruler to gently press the bend out. Hold it firmly against a flat surface for support and press down carefully on the curled corner until it lies flat. Work slowly, re-pressing as needed, to fully work out the crease without damaging the surface. Again, apply just enough pressure to reshape – you do not want to fold or crease the paper further.

When the corner is lying flat, blot away any surface moisture with a clean lint-free cloth or paper towel. Excess moisture left on the surface could lead to watermarks or weak spots in the paper. Gently wipe away droplets but do not rub vigorously which could damage printing or surfaces.

The next crucial step is allowing the card to dry flat over multiple days. Slow air drying is important to prevent the corner from curling again as it regains its original shape memory. Place weights like heavy reference books on top to keep it pressed perfectly flat. Change the books’ position every 12-24 hours to ensure even drying.

Continue drying for 3-5 days depending on paper thickness and humidity levels. In very humid conditions it may take longer. Check each day that the corner remains flat and re-press lightly as needed if it attempts to curl at all during drying. Patience is key to allow the fibers time to dry reshaped.

For extra reinforcement once dry, apply a small piece of cellulose tape to the back of the fixed corner. Make sure the tape does not touch the printed surface or edge of the card. This helps “lock in” the new flat shape and prevent future curling. Allow further drying for another full day with weights on top.

With careful, gradual humidifying and pressing followed by slow drying under weights, bent card corners can usually be successfully straightened back into proper form. Take your time and go slowly to avoid damaging the card surface or weakening the paper stock from over-moistening. Perseverance and patience leads to restoration without further harming the collectible. With the right technique, damaged cards can regain their pristine condition.