There are two ways to obtain the crackling effect, which depend on what you are trying to achieve.
Let's start with the first one.
As I said before, this kind of crackling is used to prepare the bases for decoupage, when you want an object that looks aged on purpose. Of course you can make just the crackling effect without decoupage after: the crackling effect is already nice, even without decoupage, and is very suited for furniture, frames...
This kind of technique must be done before the decoration with decoupage.
Let's see what we need, then we'll explain the work sequences.
In order to make a good work it is necessary that the surface be perfectly smoothed and clinging for the colours. So, as usual, we have to prepare the base for the colour. If we are painting a wooden object we must give a coat of woodfiller or vynil glue watered down, which has the same aim of the woodfiller. Once it has dried give a coat of white waterpaint or acrylic plaster. If necessary give a second coat. Once it has dried, smooth the surface with a sand paper.
Now we have to choose the colours. In this example I'll realize ochre cracklings on azure colour.
First of all paint the surface with the colour you have choosen for the cracklings: so in this case ochre.
Let it dry perfectly. If you think it's necessary give a second coat of ochre. Once this colour has perfectly dried spread the crackling medium on the surface using a dry clean flat brush.
Keep in mind that this medium is very gelatinous, like honey I would say, the more you lay it thin, the more the crackling will be fine and embedded, the more you lay it thick, the more the crackling will be large.
Read very carefull the instructions on the bottle of the medium, because each mark has its drying time, anyway usually this time should be around 60 minutes, then you must lay the second colour, the main colour, in this case the azure. The colour laid on the medium does crack thus letting see the colour beneath: that is ochre.
Be careful when laying the second colour: use a flat big brush and try not to overlap brushstrokes, or you might remove the medium beneath e the crackling effect won't take place.
Here are some examples of what we can do changing colours:
Once it has dried you can proceed with the decoupage decoration if you like, exactly the same way you did on the others acrylic bases.
anyway even if you don't want decoupage, I suggest you to protect the surface with a coat of varnish.
This kind of crackling is made after you have made the decoration with decoupage, or after you have painted anyway, when you want to give the object an ancient look on purpose, and the crackling you obtain with this technique is different from the previous one, besides while the cracklings of the previous technique are always in the background, that is behind the decoupage decoration, the cracklings of this technique are always in the foreground, that is before the entire composition: background and images in foreground.
Of course this kind of crackling can be used also as a finish for paintings when you are trying to achieve an ancient effect. Read carefully the instructions how to precede, because you work differently on acrylic paintings and oil paintings.
Once the decoupage is over, and after the varnish coats given as usual, you can proceed spreading the crackling varnish.
Let's see the basic technique to obtain the crackling finish.
Give a coat of flatting varnish or ageing varnish on the surface of the object decorated with decoupage or the acrylic painting.
Let it dry, but not too much, I mean the surface must be slightly sticky under your finger, yet enough dry that you don't leave your finger tips on it.
If you are working on an oil painting, just leave this step, because the oil colours is already in contrast with the crackling varnish you are going to lay.
Now give a coat of crackling varnish, or arabic gum or lac.
The crackling will make because of the incompatibility of the two varnishes which have different solving medium. Keep in mind that the crackling will be big and sparse if the first varnish is wetter, while the crackling will be thin and thick if the first varnish is drier.
Dry the surface using a phon untill will see the crackling appear.
Let the surface dry completely for some hours after the cracklings have appeared.
Now dilute some oil brown paint with turpentine and using a soft cloth spread it uniformely on the cracked surface. The brown paint will stay just inside the cracklings. Take off the excess of colour with a clean cotton cloth which doesn't leave hair and let it dry for almost a day.
Or else if you don't have the oil paint, you can use the bitumen wax.
Give a second coat of flatting varnish or ageing varnish on the dry surface in order to make it bright and waterproof.
In order to avoid disappointments try first this technique on waste objects, and change the drying time of the first varnish and its thickness.
Keep in mind that the result depends also on the humidity degree of the room in which you are working. So you can never really preview how the crackling will be.
Here is an example:
As you can see from the picture, this kind of finishing turns the colours yellow, because you had to lay two coats of flatting varnish and the crackling varnish, or the arabic gum or the lac, which are all yellowing varnishes.
This is not exactly a fault, but you might not like always this yellowing effect.
If you don't like the ageing effect of the traditional method, you should know that there are others water based products which creates the crackling without the yellowing effect.
Let's see some:
They are two products water based which are sold together and which replace the ageing varnish and the crackling varnish.
They should be used the same way described before with the traditional method, just read carefully the instructions of the two bottles, because different marks might have different drying times.
Anyway with this kind of product you must lay the second product very abundantly if you want sparse cracklings while laying the second product thin you will get thick cracklings.
This is what you can obtain:
This is a unique product which crackle by itself once it has been laid without the contrast with another varnish. It creates a thick web of cracklings thinner if the drying is longer and larger if the drying is faster, using a phon for example.
This is what you can obtain:
The good point of this product consists in the fact that you have to give just one coat of varnish to obtain the crackling.