When my girlfriend dumped me I found hobbies to busy myself in... Sadly enough, making latex scars was one of them. I am not experienced in any way, this is how I do them, they don't look amazing but some of them turn out quite realistic.

Step 1: What You Will Need

1 Bottle of Liquid Latex (check on eBay for good prices)
A Syringe (optional) Used for a fine, controled flow of latex
Medium & extra fine paint brushes
Red, dark pink & light-medium brown paints
A piece of paper for a dry brush effect
PATIENCE

Step 2: First Layer

Take your bottle of latex and syringe, if your are using one, and drawn in some liquid.

Apply a thin layer if the area you want your scar to be.
My scar is on my left wrist for ease as I have no-one as a test-subject/camera-man.

Now wait for the first layer to dry. Pass your time by doing something fun, I talked to my friends on msn and played GTA for a few minutes.

When the colour has changed slightly and you can notice an obvious change in viscossity, take a small ubber strip and press it to the surface. This creates an un-even surface, giving the scar a realistic look, otherwise it would be far too shiny.

Step 3: First Paint

Take your pink paint. the paint is pink as to replicate the colour of inflamed skin.

Take a small amount of paint and rub it into the paper to take most of the moisture away.
The brush should still have some paint on it, not dried.

gently paint the latex. The scar should not look too pink... It should just have had a slight colour change, making it look irratated.

Before proceding, let the paint dry.

Step 4: Second Layer

Next, apply a second thin layer of latex over the painted first. This will lock the colour in and stop them mixing.

Again, dab with a piece of textured rubber to create a life like appearance.

Wait for the latex to dry before moving on.

Step 5: Second Paint

Now take your brown paint.

Just like the pink, take a small amount, rub into paper and paint onto the scar.

You can probably apply a bit more brown paint than pink.

Wait for the paint to dry.

Step 6: Third Layer

Again, thin layer of latex and let dry.

This time it is really important that you blot the scar. This layer is almost the last, so make a good job.

Step 7: Third Paint

Take your red paint.

Don't paint this layer with a dry brush effect.

Just paint a long, thin line of red all the way down the scar.

The brighter the paint the better for showing up throught the protective coating.

Let it dry.

Step 8: Final Layer : Protective Coating

Add one last layer of latex ontop of the dried red paint. This will stop it from flaiking off when it moves.

Again blotting is very important as this is the LAST layer and you will not want this to shine.

When this coating is dry, your scar is finished.

Also, inbetween the first layer and the first paint, you can add small threads to make stiches.
Place your first line of latex, then first thread. Add a small drop of latex ontop of the thread to keep it down. Repeat until the scar is covered, then continue to first paint and onwards, just the exact same.