How can I make the red bricks on my fireplace look brighter?

Try scrubbing them with Krud Kutter original concentrate. It removes all oily grime. You would spray it on, let it sit a minute, scrub a little, and the spray with clear water to rinse. Lay rags along bottom of brick to catch liquid.

Once you get the brick clean, use a brick sealer made with polyurethane or acrylic. It’ll give the brick a slight sheen and bring out more of the color.

Hi Lacy, you can start by cleaning them, they likely have a good smoky buildup ion them,

How to clean bricks

How to Clean a Fireplace With Baking Soda and Dish Detergent

Is there anything baking soda can’t clean?

1. Add about 2-3 tablespoons of dish soap to about a half cup baking soda to make a paste.
2. You’re not really looking for a thick consistency, you want it to be able to spread it on the wall with ease, so you might end up adding more than 2 tablespoons of soap.
3. Dip your scrub brush into the paste and scrub in small circular motions from the bottom of the brick up, to avoid streaks.
4. Let the mixture set on the wall for a few minutes before rinsing with warm water. Repeat the steps if necessary.

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(Image credit: Ashley Poskin)

After the side walls of the fireplace have been cleaned, finish up by washing the bottom of the fireplace and the hearth. Keep old rags on hand to soak up any dirty water that has run off from scrubbing the walls, then apply your cleanser, scrub, rinse, and repeat until clean.

If they are not bright enough, you can paint them

Prep. Use the widest painters tape you can find and tape off any areas that you don’t want painted. In my case it was marble, in yours it could be the wall behind the brick. Lay out a drop cloth, or paper around the area where you will be working to protect the floor and catch any paint that strays.

Prime with high heat primer: get down into the grooves of the mortar joints with your paintbrush. Don’t worry about perfect brush strokes at this point, just make sure to cover the entire surface. I don’t even bother with a roller brush this early in the game — your paint brush will allow you to get back into all the corners and cover all the uneven areas.

Paint it: Any other color you choose, of course! Start with the back, get in the corners and work your way forward. Keep your brush in hand, don’t even worry about your roller yet. If your topcoat is darker than your primer you’ll want to be sure you get the brush into all the grooves and any pitted areas for complete coverage.

let dry and repeat for second coat

To be certain you really want to "brighten and make more colorful" I suggest you take a pic and lay over color to look at it. IMHO doing this may make you change your mind! Everyone is trying to downplay old style red brick these days.