Due to a few posts talking about scratches etc I thought I would post this as it helps understand what you are trying to do when removing swirls or a scratch (again I've borrowed it from another website)
</font>
<b style="font-size: 13px; ">IN THEORY[/b]
Here we look at the theory behind machine polishing – what exactly is going on – to see how we can best hone practical technique to get the best out of your machine investment. The descriptions here apply to generic polishes that you will find on the market, though all do differ slightly in their characteristics.</font>
<i style="font-size: 13px; ">PAINT SYSTEMS[/i]
Shown in the picture below are the two typical paint systems you are likely to encounter when detailing: “single-stage” and “clear-coated”.</font>
<div align="center" style="font-size: 13px; ">
In all cases when machine polishing a car, you are working on the top layer of paint. You cannot remove more than this layer – indeed, you should always leave a healthy thickness of the top most layer. This puts a restriction on the defects which can be removed – any deep marks which go through the top layer of paint cannot be removed.</font>
<i style="font-size: 13px; ">PAINT DEFECTS[/i]
The paint defects that you may encounter are shown in pictures earlier on. We look at these in a little more detail here – for full descriptions please see separate guide.</font>
<ul style="font-size: 13px; "><li style="font: normal normal normal 10ptormal verdana, geneva, lucida, 'lucida grande', arial, helvetica, sans-serif; ">Swirl Marks are light and shallow scratches covering large areas of the paintwork, typically inflicted by poor wash technique.<li style="font: normal normal normal 10ptormal verdana, geneva, lucida, 'lucida grande', arial, helvetica, sans-serif; ">Random Deep Scratches (RDS) are deeper scratches into the paintwork, typically inflicted by grit being dragged along the paint, or minor key scratches.<li style="font: normal normal normal 10ptormal verdana, geneva, lucida, 'lucida grande', arial, helvetica, sans-serif; ">Severe Scratches are marks which go through one or more of the paint layers, sometimes down to the bare metal – these cannot be sorted by machine polishing and require painting (minor filling or section respray) to fix.<li style="font: normal normal normal 10ptormal verdana, geneva, lucida, 'lucida grande', arial, helvetica, sans-serif; ">Oxidisation happens generally to cars with no clear coat and causes the paint to fade and look dry[/list]
Shown in the picture below is a schematic of the typical paint defects.</font>
<div align="center" style="font-size: 13px; ">
<i style="font-size: 13px; ">REMOVING DEFECTS USING ABRASIVE POLISHES/COMPOUNDS[/i]
The most popular way of removing paint defects by machine is to use an abrasive polish. When worked into the paint, the abrasives cut away a layer of the paint where the defects are. Once the amount of paint removed is deeper than the defect, the defect will have been removed. It is like “re-flattening” the paint to a level where no defects exist.</font>
As mentioned above, when first approaching a car, always start with one of the lightest polish and pad combination that you have. This will remove only a small amount of paint, but may be enough if you have soft paint or only light swirls. Shown in the picture below are the above defects after being tackled with a typical light polish and pad combination (for example Menzerna PO85RD Final Finish on a Meguiars W8006 Polishing pad).</font>
<div align="center" style="font-size: 13px; ">
A thin layer of paint has been removed with the light cutting polish and soft foam pad. The combination has removed a lot of the lighter swirl marks, but has left the deeper swirl marks and the RDS and severe scratch. It is clear that there is still a healthy thickness left (can be checked with a paint thickness gauge in practice). So we would progress up the ladder to a more moderate cutting combination now to see if we can get better correction. For example, we may step up to Menzerna PO85RD3.02 Intensive Polish on a Meguiars W8006 Polishing pad to get the results shown in the picture below.</font>
<div align="center" style="font-size: 13px; ">
A thicker layer of paint has been removed and we have no fully corrected the swirl marks, both light and deep. The RDS remain however as it is much deeper into the clear coat. If the paint thickness permits we may wish to tackle the RDS with a heavier cutting combination to remove yet more paint. An example of this may be Menzerna POS34A Power Gloss on a Meguiars W7006 Cutting pad, to get the results shown in the picture below.</font>
<div align="center" style="font-size: 13px; ">
We can see that yet more paint has been removed by this process, however the RDS has been successfully removed. Great care must be taken when using compounds and removing large amounts of paint as leaving the clear coat too thin can cause it to flake off. Clearly the severe scratch cannot be removed as it goes through both the clear coat and colour coat layers.</font>
When working up through the abrasive scale to find the best possible combination for the paint it is worthwile bearing in mind that some of the marks that may be in the paint are too severe to remove safely. Always aim to leave as much clear coat (or colour coat on a two stage paint job) as possible. There are many reasons for this, just a couple are: if the uppermost layer is too thin, it can flake off and the only repair is a respray; if only a thin layer of clear coat is left then it will not be possible to machine polish the finish again with abrasives top remove any marks that may be inflicted at a later date.</font>
Perfection is a wonderful goal to aim for – but always bear in mind the safety of the combinations you are using for the finish you are using them on. This also applies if the paintwork seems soft – use of a compound on soft paintwork can remove large amounts of paint very quickly. So if you choose to use a compound on a car with soft paintwork, be sure to monitor the paint thickness regularly during the machine polishing process – after every few passes.</font>
<i style="font-size: 13px; ">REMOVING DEFECTS BY ROUNDING EDGES[/i]
This method is one which can be used with a moderate degree of success in situations where full removal of deeper marks is not possible for whatever reason (for example, paintwork is too thin). The machine polishing process can naturally round off the edge of marks on the paintwork as shown in the picture below.</font>
<div align="center" style="font-size: 13px; ">
The sharp edges of the deep mark catch the light and it is reflected back in an intense ray allowing you to clearly see the scratch in the finish. When the edge has been rounded off, there is no intense reflection of the light. It is instead spread over a wider area and it doesn’t appear as easily to the eye that there is a deep scratch there.</font>
This process is not fully removing the marks in the paintwork. Instead it is making them harder to see by essentially softening the edges, which acts to scatter the light rather than reflect it. This in turn makes it harder for the eye to see the marks. They are not fully hidden, but they appear a lot less severe.</font>
<i style="font-size: 13px; ">REMOVING DEFECTS BY FILLING[/i]
In some cases it is simply not possible to remove the swirls with an abrasive polish, for example if the upper most paint layer is too thin. Using a product with fillers gives another option in these situations – the defects are not removed, but instead they are masked by using fillers as shown in the picture below.</font>
<div align="center" style="font-size: 13px; ">
We can see that the original swirls above are quite deep compared to the thickness of the clear coat. Fully removing them by removing the paint would leave only a very thin layer of clear coat and this is something we would want to avoid doing. The alternative shown above is using fillers to mask the swirls. Not all swirls will be filled in perfectly, so complete correction using fillers will likely not be possible. However a significant improvement can be made without risking the paint.</font>
An issue with filling swirls is the solution is not permanent. Over time the fillers will be removed by washing and general wear and this will result in the swirls returning.</font>
<i style="font-size: 13px; ">THE POLISHING PROCESS[/i]
Here we look at how the polishes work the remove the paint defects as discussed above, with a description of the best generic techniques to work machines and polishes.</font>
Polishes which use a mechanical abrasive to remove the paint (most on the market including Meguiars, 3M, Menzerna, Poorboys, Optimum, Chemical Guys…) typically use a “powdered” abrasive carried in a solution with lubricant. The polish contains little abrasive particles which act under the action of the pad which moves them across the paint to slice off a little amount of the paint. It is quite similar to exfoliating the skin on your face with a facial scrub.</font>
In many polishes which are widely available, the abrasives break down under the action of cutting to become finer and finer. This means that as you polish, the amount of paint removed gets less and less. Shown in the picture below is a schematic of how this works in practice.</font>
<div align="center" style="font-size: 13px; ">
With the first passes of the machine across the paint, the abrasives are cutting a large amount of the paint away. As the polish is worked, the abrasives break down and the amount of paint removed gets smaller and the finish finer. Towards the later stages of the polishing set the abrasives have broken down to a point where they are removing only a very small amount of paint with each pass. The finish is now also much finer than at the beginning. The abrasives have diminished from heavy cutting through to fine finishing.</font>
It depends on the polish being used how aggressive the initial cut is and how fine the final refining is. Typically, a finishing polish (such as Meguiars #80, Poorboys SSR1) will have very light initial cut but a very fine finishing cut to deliver a sharp finish. An aggressive compound (such as Menzerna Power Gloss, 3M Fast Cut) will have strong initial cut but will not break down to a very fine finishing, thus resulting in a less sharp finish.</font>
Not all polishes break down in such a fashion however. Some polishes remain aggressively cutting throughout the set and for this reason they will require to be followed with a fine cutting finishing polish. Other polishes rely more on the cut of the pad to determine the level of cut and quality of finish, an example of which is MarkV Mystique. These latter polishes can be used on wool pads on rotary polishers to deliver significant correction. By dual action polisher they can deliver high levels of correction on a cutting foam pad, and lower levels of correction but fine finishing on a polishing foam pad.</font>
The use of different grades of foam pad will also affect the cut ad final finish delivered by a polish, the amount of which depends very much on the polish. For many light to medium polishes, the use of a polishing pad is generally sufficient and a more aggressive pad will not deliver that much extra.</font>
However for more moderate cutting polishes, the use of cutting foams can give a better cut and allow the abrasives to cut better. The flip side is that the more aggressive cutting foams can also leave marring of their own on a paint finish necessitating a follow up with a finishing polish to refine the paintwork.</font>
The levels to which pads and polishes cut and finish also depends greatly on the paintwork being tackled. Only by experimenting on a test section can you fully ascertain what each combo will do. For example, on some harder paints the use of a finishing polish on a finishing foam delivers very little if any discernable difference in quality of finish over the use of a medium cutting polish on a polishing foam pad. However on a softer paint which is more sensitive to the abrasives, it may be a completely different story, with big gains to be had by using a fine finishing combo to follow a more aggressive pair of products.</font>
</font>
<b style="font-size: 13px; ">IN THEORY[/b]
Here we look at the theory behind machine polishing – what exactly is going on – to see how we can best hone practical technique to get the best out of your machine investment. The descriptions here apply to generic polishes that you will find on the market, though all do differ slightly in their characteristics.</font>
<i style="font-size: 13px; ">PAINT SYSTEMS[/i]
Shown in the picture below are the two typical paint systems you are likely to encounter when detailing: “single-stage” and “clear-coated”.</font>
<div align="center" style="font-size: 13px; ">

In all cases when machine polishing a car, you are working on the top layer of paint. You cannot remove more than this layer – indeed, you should always leave a healthy thickness of the top most layer. This puts a restriction on the defects which can be removed – any deep marks which go through the top layer of paint cannot be removed.</font>
<i style="font-size: 13px; ">PAINT DEFECTS[/i]
The paint defects that you may encounter are shown in pictures earlier on. We look at these in a little more detail here – for full descriptions please see separate guide.</font>
<ul style="font-size: 13px; "><li style="font: normal normal normal 10ptormal verdana, geneva, lucida, 'lucida grande', arial, helvetica, sans-serif; ">Swirl Marks are light and shallow scratches covering large areas of the paintwork, typically inflicted by poor wash technique.<li style="font: normal normal normal 10ptormal verdana, geneva, lucida, 'lucida grande', arial, helvetica, sans-serif; ">Random Deep Scratches (RDS) are deeper scratches into the paintwork, typically inflicted by grit being dragged along the paint, or minor key scratches.<li style="font: normal normal normal 10ptormal verdana, geneva, lucida, 'lucida grande', arial, helvetica, sans-serif; ">Severe Scratches are marks which go through one or more of the paint layers, sometimes down to the bare metal – these cannot be sorted by machine polishing and require painting (minor filling or section respray) to fix.<li style="font: normal normal normal 10ptormal verdana, geneva, lucida, 'lucida grande', arial, helvetica, sans-serif; ">Oxidisation happens generally to cars with no clear coat and causes the paint to fade and look dry[/list]
Shown in the picture below is a schematic of the typical paint defects.</font>
<div align="center" style="font-size: 13px; ">

<i style="font-size: 13px; ">REMOVING DEFECTS USING ABRASIVE POLISHES/COMPOUNDS[/i]
The most popular way of removing paint defects by machine is to use an abrasive polish. When worked into the paint, the abrasives cut away a layer of the paint where the defects are. Once the amount of paint removed is deeper than the defect, the defect will have been removed. It is like “re-flattening” the paint to a level where no defects exist.</font>
As mentioned above, when first approaching a car, always start with one of the lightest polish and pad combination that you have. This will remove only a small amount of paint, but may be enough if you have soft paint or only light swirls. Shown in the picture below are the above defects after being tackled with a typical light polish and pad combination (for example Menzerna PO85RD Final Finish on a Meguiars W8006 Polishing pad).</font>
<div align="center" style="font-size: 13px; ">

A thin layer of paint has been removed with the light cutting polish and soft foam pad. The combination has removed a lot of the lighter swirl marks, but has left the deeper swirl marks and the RDS and severe scratch. It is clear that there is still a healthy thickness left (can be checked with a paint thickness gauge in practice). So we would progress up the ladder to a more moderate cutting combination now to see if we can get better correction. For example, we may step up to Menzerna PO85RD3.02 Intensive Polish on a Meguiars W8006 Polishing pad to get the results shown in the picture below.</font>
<div align="center" style="font-size: 13px; ">

A thicker layer of paint has been removed and we have no fully corrected the swirl marks, both light and deep. The RDS remain however as it is much deeper into the clear coat. If the paint thickness permits we may wish to tackle the RDS with a heavier cutting combination to remove yet more paint. An example of this may be Menzerna POS34A Power Gloss on a Meguiars W7006 Cutting pad, to get the results shown in the picture below.</font>
<div align="center" style="font-size: 13px; ">

We can see that yet more paint has been removed by this process, however the RDS has been successfully removed. Great care must be taken when using compounds and removing large amounts of paint as leaving the clear coat too thin can cause it to flake off. Clearly the severe scratch cannot be removed as it goes through both the clear coat and colour coat layers.</font>
When working up through the abrasive scale to find the best possible combination for the paint it is worthwile bearing in mind that some of the marks that may be in the paint are too severe to remove safely. Always aim to leave as much clear coat (or colour coat on a two stage paint job) as possible. There are many reasons for this, just a couple are: if the uppermost layer is too thin, it can flake off and the only repair is a respray; if only a thin layer of clear coat is left then it will not be possible to machine polish the finish again with abrasives top remove any marks that may be inflicted at a later date.</font>
Perfection is a wonderful goal to aim for – but always bear in mind the safety of the combinations you are using for the finish you are using them on. This also applies if the paintwork seems soft – use of a compound on soft paintwork can remove large amounts of paint very quickly. So if you choose to use a compound on a car with soft paintwork, be sure to monitor the paint thickness regularly during the machine polishing process – after every few passes.</font>
<i style="font-size: 13px; ">REMOVING DEFECTS BY ROUNDING EDGES[/i]
This method is one which can be used with a moderate degree of success in situations where full removal of deeper marks is not possible for whatever reason (for example, paintwork is too thin). The machine polishing process can naturally round off the edge of marks on the paintwork as shown in the picture below.</font>
<div align="center" style="font-size: 13px; ">

The sharp edges of the deep mark catch the light and it is reflected back in an intense ray allowing you to clearly see the scratch in the finish. When the edge has been rounded off, there is no intense reflection of the light. It is instead spread over a wider area and it doesn’t appear as easily to the eye that there is a deep scratch there.</font>
This process is not fully removing the marks in the paintwork. Instead it is making them harder to see by essentially softening the edges, which acts to scatter the light rather than reflect it. This in turn makes it harder for the eye to see the marks. They are not fully hidden, but they appear a lot less severe.</font>
<i style="font-size: 13px; ">REMOVING DEFECTS BY FILLING[/i]
In some cases it is simply not possible to remove the swirls with an abrasive polish, for example if the upper most paint layer is too thin. Using a product with fillers gives another option in these situations – the defects are not removed, but instead they are masked by using fillers as shown in the picture below.</font>
<div align="center" style="font-size: 13px; ">

We can see that the original swirls above are quite deep compared to the thickness of the clear coat. Fully removing them by removing the paint would leave only a very thin layer of clear coat and this is something we would want to avoid doing. The alternative shown above is using fillers to mask the swirls. Not all swirls will be filled in perfectly, so complete correction using fillers will likely not be possible. However a significant improvement can be made without risking the paint.</font>
An issue with filling swirls is the solution is not permanent. Over time the fillers will be removed by washing and general wear and this will result in the swirls returning.</font>
<i style="font-size: 13px; ">THE POLISHING PROCESS[/i]
Here we look at how the polishes work the remove the paint defects as discussed above, with a description of the best generic techniques to work machines and polishes.</font>
Polishes which use a mechanical abrasive to remove the paint (most on the market including Meguiars, 3M, Menzerna, Poorboys, Optimum, Chemical Guys…) typically use a “powdered” abrasive carried in a solution with lubricant. The polish contains little abrasive particles which act under the action of the pad which moves them across the paint to slice off a little amount of the paint. It is quite similar to exfoliating the skin on your face with a facial scrub.</font>
In many polishes which are widely available, the abrasives break down under the action of cutting to become finer and finer. This means that as you polish, the amount of paint removed gets less and less. Shown in the picture below is a schematic of how this works in practice.</font>
<div align="center" style="font-size: 13px; ">

With the first passes of the machine across the paint, the abrasives are cutting a large amount of the paint away. As the polish is worked, the abrasives break down and the amount of paint removed gets smaller and the finish finer. Towards the later stages of the polishing set the abrasives have broken down to a point where they are removing only a very small amount of paint with each pass. The finish is now also much finer than at the beginning. The abrasives have diminished from heavy cutting through to fine finishing.</font>
It depends on the polish being used how aggressive the initial cut is and how fine the final refining is. Typically, a finishing polish (such as Meguiars #80, Poorboys SSR1) will have very light initial cut but a very fine finishing cut to deliver a sharp finish. An aggressive compound (such as Menzerna Power Gloss, 3M Fast Cut) will have strong initial cut but will not break down to a very fine finishing, thus resulting in a less sharp finish.</font>
Not all polishes break down in such a fashion however. Some polishes remain aggressively cutting throughout the set and for this reason they will require to be followed with a fine cutting finishing polish. Other polishes rely more on the cut of the pad to determine the level of cut and quality of finish, an example of which is MarkV Mystique. These latter polishes can be used on wool pads on rotary polishers to deliver significant correction. By dual action polisher they can deliver high levels of correction on a cutting foam pad, and lower levels of correction but fine finishing on a polishing foam pad.</font>
The use of different grades of foam pad will also affect the cut ad final finish delivered by a polish, the amount of which depends very much on the polish. For many light to medium polishes, the use of a polishing pad is generally sufficient and a more aggressive pad will not deliver that much extra.</font>
However for more moderate cutting polishes, the use of cutting foams can give a better cut and allow the abrasives to cut better. The flip side is that the more aggressive cutting foams can also leave marring of their own on a paint finish necessitating a follow up with a finishing polish to refine the paintwork.</font>
The levels to which pads and polishes cut and finish also depends greatly on the paintwork being tackled. Only by experimenting on a test section can you fully ascertain what each combo will do. For example, on some harder paints the use of a finishing polish on a finishing foam delivers very little if any discernable difference in quality of finish over the use of a medium cutting polish on a polishing foam pad. However on a softer paint which is more sensitive to the abrasives, it may be a completely different story, with big gains to be had by using a fine finishing combo to follow a more aggressive pair of products.</font>