We repainted a wall in our home. We used some paint remaining from the past (painted 4 years ago). Our intent was to keep a gallon for touch ups. However, the paint is lighter, in color, than the surrounding walls. Same paint, same mix lot. Painted 24 hours ago.

Will it darken?

It should dry darker than when it first goes on, but if the can is four years old I am not sure

Existing walls have a lot of dirt on them in last 4 years. Try cleaning the walls before touch up. Depending on the color, type, qaulity, etc. of the paint, the pigments in the paint may get darker in time.

Skilberger may be right. The wall may be the same color as the others were when painted. Scrub them. The pigments other than the titanium dioxide in the paint may have flocculated. Never mind what that means, they just have gotten old and aren't doing their job leaving the paint lighter.

Thanks for your responses.

I did not know that flocculation could occur in a cured compound. WOW - learned something new - cool.

I will try washing the walls. I gave them a quick wipe down before paint but I will use a solvent (mild soap). Either way I will post up my results.

Ciao

There have been a couple of things that have happened:

Lilfyre is correct, the paint will darken somewhat as it dries and cures.

SkiBerger is also correct, the existing paint on the walls have become dirty over the past 4-years. Cleaning the walls before painting is highly recommended. If you are using soap, besure to rinse it thoroughly and let it dry overnight.

Labman's Flocculation comment also seems correct (he is a Chemist I believe).

Also, the existing paint has aged either by oxidation or by reaction to UV.

As a former Depot Paint Geek, we ran into problems like this all the time. I would suggest doing the following:

Mix the paint thoughly (need to prevent flocculation) so that the pigments, binders and flattening agents are complete dispersed.

Wash the wall that needs to be touched up and rinse completely and allow to dry over night.

Paint the area that needs to be touched up (or, and much preferred, paint the whole wall.

Allow paint to dry and cure a few days before worrying about the color/sheen difference.

Good luck, Dan