Below is an easy way to make a blood brush look realistic using Photoshop. It's perfect for dark art, and such.
First and foremost, use the original black and white, and the brush at full opacity for your blood. You can change the opacity at the END if you choose to make it partially see-through. Try to only use brushes with a lot of detail (shadows and highlights) to achieve a real look. Stay far, far away from flat, toneless blood brushes if you want them to look even slightly real.
Once you've made a new layer (shift + cntrl + N) in your artwork, resize and use the brush. (Make sure there is a white background on ANOTHER layer so that the tones and colours will look proper).
It should look like this:
Next, with the layer with the blood on it selected, go to 'color balance' (ctrl + B). Put the values to:
This will make your blood look something like this:
To add dimension to your blood, go to 'curves' (ctrl + M), and manipulate the curve to look something like this, but use your own discretion:
When/if more colour is added later, the darkness may go away, but if it's near black, ease back on the curve. This is how the 'blood' should look:
If the image is too dark, as above, go to the 'color balance' again (ctrl + B). Adjust the values to suit what you want the blood to look like. The colour should look slightly better. If you're happy with the blood, it is ready to be used.
However, if you're looking to make further impact, you can also burn and dodge the edges to add some drama.
The 'burn' tool will allow you to make the edges darker, while the 'dodge' tool will allow you to make the edges lighter. Be sure to take into account the direction of the lighting.
THANK YOU TO Shad0w-GFX ON DEVIANTART (
Shad0w-GFX on deviantART) FOR THE BRUSH USED FOR THE BLOOD. If you find any of the steps here confusing at all, take a look at his version. Also, the brushes he has are very high quality, and I suggest taking a good look at them.
Hope this helped you out! If you need any help at all, feel free to message me!