How to hide the joins!
Small repairs may not warrant spraying a complete panel. In this case consider what will be the easiest way to "lose" the edges of your paint repair. This will ideally be a slim rear pillar or narrow section of bodywork, or a moulding or break line further along from the repair. If using basecoat and clear, it is usually easier and quicker to lacquer complete panels, or if spraying for example a door, blend and lacquer the panels either side of your repair to completely hide any slight colour difference.
Thoroughly flat all areas to be blended or lacquered with ultra-fine abrasive pads (usually grey Scotchbrite), nothing any coarser. If lacquer is to be blended away up a rear pillar or suchlike, use a fine grade compound to restore the gloss to the last few inches of the abraded area
Apply colour coats to the repair area until covered, preferably using a lower pressure than usual to reduce overspray. To blend the colour into surrounding areas apply two or three extra coats, extending the colour coats a few inches further out for each coat. Always keep within the abraded area. If paint strays on to unsanded paintwork it will always compound back to a visible edge. Arcing the spraygun at the edges of each coat helps the paint edge to fade away, rather than a sharper cut-off to the colour. Finally, melt the overspray edge with a very light coat of thinners, so that the edge of the repair can be compounded into the original paintwork without trace.
Blending colours to hide subtle colour differences
Metallic colours are unusual in that different shades can be produced from the same batch of paint by varying application methods or conditions, For this reason blending basecoat and clear metallics is almost compulsory to ensure a perfect match. For most brands of basecoat exactly the same blending process as solid colours is used.
The basecoat colour may be blended into adjacent panels to achieve a perfect colour match. Spray two or three coats of colour onto the repaired area until covered. Extend the basecoat over a slightly larger area to loose any colour differences. It may be easier to reduce air pressure for these coats, which will help to minimize a dark, rough edge where the aluminium particles stand up from the panel instead of laying flat. Do not apply thinners to blend the basecoat edge.
After leaving the basecoat to dry for 5-10 mins, lacquer can be applied. Lacquering the full panels is usually a lot easier than trying to blend a large area mid-panel.
If the repair must be blended into a part panel, the same requirements as for solid colours must be met. The final coat of lacquer must stay within the area that has been sanded with Scotchbrite or similar abrasive pads,otherwise it will be impossible to compound away the lacquer edge. A light coat of thinners to the lacquer edge will blend the repair into the existing paintwork. When hard, do not aggressively compound the lacquer joint - light compounding produces better results.