Even if you are an experienced collector, it is important to be aware of restoration.
There are tens of thousands, probably hundreds of thousands or American comic books that have been restored in some way. It is far less evident for British comics. A British comic or annual would have to be pretty high value owing to the expense incurred. It could also be that vintage British comic paper would be harder to match as well.
The most common instances of restoration are usually restored spines on very early Dandy, Beano and Rupert Books. You might also get comics that have had rusty disintegrating staples removed and paper fibre used to repair the damage. Most of the following remarks are concerned with American comic books but they could apply to British comics up to a certain point.
There is an argument for highly skilled, professional restoration. If a high value or particularly rare comic book is in such a state that, if left alone, will continue to deteriorate to the point of being lost, then it would be sensible to save it. What all collectors should be wary of is amateur attempts at restoration which have usually resulted in a comic book being ruined forever. The most common is colour touch up, usually using a black felt tip pen, along spine areas. Other specific examples of restoration to look out for are listed below.
It is interesting that the Certified Guarantee Company (CGC) ocasionally ignores a microscopic colour touch or the tiniest amount of dried glue on the spine as restoration. CGC tends to give these comics a Blue or Universal (Unrestored) label. Note that this is really the slightest degree of a defect and any more than that, CGC would incline towards a Restored label.
In the last few years or so, the practice of pressing has become big business in America. This involves taking a high grade comic book in, say, a 9.0 Very Fine/Near Mint and literally pressing it to improve the register, the flatness, the appearance of the cover. A 9.0 may be re-graded and come out as a 9.2. For key and major key issues, this could be a difference of hundreds, even thousands of dollars.
Restored American comic books went through a period of backlash a few years ago but in recent times they are making something of a comeback. You can understand why. A very pretty-looking restored Fantastic Four #1, for example, is currently a fraction of the equivalent grade in unrestored condition.
If you are unsure about restoration, ask questions. These are some of the more frequent restoration subject areas:
Look closely at the spine and dark/black areas of the cover. Felt tip pen will bleed through the cover and leave spots of black on the pages inside. Professional colour touch is much harder to spot, although ultra-violet light will reveal much.
Look for white or Typex-like glue around the spine, usually on the inside front cover. Very thin sugar paper can also be used to reinforce an area where the cover has pulled away from a staple.
This is the closing of minor tears and nicks in covers and pages using paper fibres. Very tough to see if very expertly done though more obvious if done by an amateur.
Corners tend to become rounded or lose tiny chips so paper can be added to make them sharp and perfectly square. This is usually fairly easy to spot from the inside.
Some comic books may have one or even all three sides trimmed by a guillotine to do away with Marvel chipping or some other edge imperfection. This is a serious defect. The giveaway is a perfectly flat right-hand edge which would otherwise be more v shaped.
Evidence of browning pages having been lightened or even whitened with chemicals. A distinct chemical smell usually gives the game away.
Where covers are lightened to give an almost unnatural, white brilliance. Lots of Fantastic Four #1s and X-Men #1s have been bleached and are among the most famous white covers of them all.
Where there was once a spine roll, this has been flattened out and weaker paper has had to be reinforced with acrylic, often giving a much stiffer feel to the paper. This practice is dying out as restoration techniques in general have become much more sophisticated.
This is where the cover and the interior from two different copies are 'married' together to produce a higher grade copy. You might spot this from looking at the three edges to see how the interior sits in its new cover. It might not quite match up and may have had a little trimming to make it fit.