hi, it sounds like the nail art polish you are using may be old and too thick, thus it is resulting in the polish not drying quickly or thoroughly - so when you applying the top coat it is smudging and blurring the nail art :o)
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Apply a bead of polish to the cuticle area and then drag down towards the free edge without the brush touching your nail art. The action looks as though the brush is floating on top of the bead of polish. The angel of the brush should be lower than you would normally use to paint your nails. Regular top coats are thinner and stand more chance of messing up your art work. Remember to allow it to dry before applying top coat for best results.
If your nail art isn't dry after 3 hours it may be that you have oil from your skin & nails "contaminating" the polish, this stops it from drying. Also, check the age of the polish, the thickness of application, the environment..is it hot in the room where you do your nails? Try a different brand of polish...Orly is excellent and they do a spritz dry which dry's the polish quickly and the top and base coat are excellent quality.
The nail art must be fully dry before top coating,this may be your problem :)
It could be the quality of the top coat or not allowing the colour to dry properly before adding nail art and then a top coat before that's dry.
It depends on what you are using to do your nail art? It might be a problem of the polish underneath.