There are often sections of a painting that will need a hard edge. Although you can paint up to the edge, keeping a definite line can be difficult.
It is usually a better idea to mask off an area, paint the section that borders it, remove the mask and complete the painting.
Masking Options
When masking an area you have a few choices.
Masking Fluid
You can use masking fluid which is like a liquid plastic and is painted on.
Top Tip use an old brush to apply masking fluid as it can be difficult to clean completely from the brush.
Let the masking fluid dry then paint the surrounding area. Once the paint is completely dry remove the masking fluid. Do not leave it on overnight or it can be hard to get off without damaging the painting surface.
Masking fluid is handy for curved and irregular shapes.
Masking Tape
I like to use masking tape. It is especially good for horizon lines in seascapes. The best part about masking tape is that you can remove it once you are confident that the paint is dry enough not to run.
However if you are painting on a paper surface it can sometimes pull the painting surface if you are not very careful when you remove it. Be careful when removing it.
I find it works very well on canvas and canvas panels. In this sketch I used it around the edges to give the finished painting a clear border.
Card Mask
Another method, and probably the easiest one when you are using a paper painting surface, is to use a piece of card. I usually end up using a piece of card from the breakfast cereal packet!
This method works best when you are using a dry brush technique, you do not want the paint too thin or it will flow beneath the card mask.
You could use it for painting in hedges in between fields in a landscape. This makes painting in hedgerows really quick. Just place the card, paint in the hedges, remove the card and paint in the field. Paint in the field while the hedge is still damp and you can blend the bottom of the hedge with the field colour for a lovely effect.
Another good example is using it to mask off the roof when you are painting shrubs and trees behind the roof line of a building. (This is shown in the illustrations).
All you need to do is cut a piece of card and hold it to mask off the roof while you use quite a dry paint to indicate the trees to the rear of the building.
Tip I find that that a card mask works best for short distances, using a large piece of card can be a bit awkward. I prefer to use a shorter piece of card and move it along as I paint.
Both of these examples use a straight edge on the card; however you could also cut the card into any shape you want for different uses. The key is not to use too wet a paint which would bleed behind the card and ruin the effect.
Which is best?
Your final choice will probably depend on the painting surface you are using.
A Word of Warning
Remember that acrylic paints are adhesives once dried. If you use a mask with very thick paint it may be stuck into the painting. Perhaps not the look you were trying for!
This is most likely to happen with masking fluid because it is removed once the paint is dried.
However, masks are very useful when using the paints more thinly and especially when using watercolour techniques.
In this quick sketch I used masking tape around the picture.
I used a card mask (second picture) for the hedges in the fields and for the building to keep the paper where the building will be clean. This is very handy when using the paint in thin washes of colour.
