Yes!!! I've been dying to get my hands on this one! Mark Harrison's brilliant Ratfink cover to Megazine 330. Mark always gives good value in his commentaries, with this entry racking up an amazing 22 images, a plethora of tips and even some photoshop brushes, wow! 
So, strap yourselves in while I hand you over to Mark! The images are numbered to help with the commentary...
"01: Running dry of the essential lube, I tapped Tharg for a much needed 
cover piece and he provided me with this meg cover to do. The only 
problem was, the script hadn't been completed yet! (Covers are usually 
the last thing to be done- not the first). Given a brief outline of the 
scene; Dredd facing rats, I delved into my almost memory to recall a 
film I hadn't seen but had a memorable photo of in my big book of horror
 movies from my childhood. The film is "Willard" (not the remake)  a 
scene that features Earnest Borgnine being set upon by rats. It's got 
great lighting and I thought i could use it as the basis of the Dredd 
cover."
01:  Yuck! No wonder Rita Tushingham didn't get on with him...
"02: I scribbled out a rough sketch in the computer for size, Dredd to be
 lying on the floor, Lawgiver drawn. (The blue pencil line look is a 
Photoshop  action (more on those later)  I got from  a Freddie E 
Williams guide book to "Digitally Drawing Comics" (buy it 
here, listen to a 
podcast about it here!) which has some very 
useful tips to black and white line art drawing, especially at the 
sketching stage. Highly recommended to aspiring and long in the tooth 
comic artists."
02: The initial Lawgiver sketch...
"03: Fleshing out Dredd wear, I lost the gun in favor of the boot knife. 
We have loads of "Dredd with gun" covers but Dredd with a knife is more 
intimate and up close  personal. "
Boot Knife!" 
03: "Bootknife!" 
04: I wanted to frame Dredd at the centre of shattered flooring, like he
 had fallen down into a rat infested basement. Ahh... that taken me back
 to reading the just released James Herbert's  "The Rats" which formed 
part of my teen literature. Great book. Terrible film. 
I planned to have out-of-focus rats silhouettes in the peripheral 
 foreground with a carpet of rats attacking from all directions in the 
low angle lit basement (The shattered floor framing also helped having 
not to draw/paint loads of rats)
04: A carpet of rats! 
"05: I always try to give old green bonce the illusion of choice and that
 I'm doing hard work so I did another sketch that was pure Dredd humour 
in my opinion. "You Dirty Rat" was the absurd idea of holding 
(literally) a rat to book. A sort of "come along quietly" moment, Dredd 
pressing the Law even to the rodents of Mega City One. But I didn't push
 this image too hard as I couldn't shake off the niggling fear that this
 had been done before. I'm sure some fan can prove this one way or the 
other bit it just felt "familiar".  (Occupational hazard doing a Dredd 
cover; am I subconsciously copying someone else?)" 
Hmmmm, none spring to mind, the closest I can think of is Cam Kennedy's classic "You're Jaywalking Citizen!" from the 1986 2000AD annual, however that certainly wasn't to a rat! - Pete.
 05: Dirty, yellow-bellied rat!
"06: Talking of copying someone else, I had in mind a painting style I 
wanted to do; more comic book than previously. To that end I referenced 
these two analogue covers of Dredd by Jock and Simon Bisley. I love the 
looseness of Jock's painting (he doesn't do enough color work) and the 
distressed texture background and Simon's colorful dynamic shot of Dredd
 and  great composition/negative space. I wanted that punchy comic book 
colouring."
06: Jock and Bisley, truly inspirational! 
"07a, b:  I already knew I wanted to have a go at trying to replicate 
entirely digitally the painting style I used back in ye olden days 
(early 1990's). In truth I've already been doing this, but this time I 
wanted to build the image up from the canvas up and use as many sampled 
real world tools and techniques as possible.  The best way to achieve 
that is to scan in some actual old painted art and build the digital 
brushes to replicate the real world painting. The scanned art shows you 
line width, the roughness of the painting, the spatter droplet size, 
etc, that can be difficult to accurately gauge when the computer can get
 you "too close" to the art sometimes. Part of my process is defeating 
the "perfectness" of computer art and build in predictably randomness. 
If that sounds like a contradiction, what I mean is achieve a "digital" 
noise in the digital toolset that best describes the factors that affect
 drawing on paper such as texture of the paper itself, angle of the pen 
etc.  Stuff that outside the computer years of practice gets you used 
to. Like those of so lovely issues we had to deal with.  (Pen snag! 
Clogged airbrush! White out!)  Now I want the look without the hassle.
The way I used to work, and many other painting comic artists was 
putting down a dark foundation over line art. In my case I use to use 
permanent marker or biro, with colored ink washes and black acrylic 
making up the foundation. You can usually see this base in the shadows, 
in this example under the arm of he muscular guy (seen here 1:1 ). Then 
I'd paint the lighter tones and colors over this with opaque acrylic. To
 create texture I might spatter ink from a primed toothbrush into the 
shadow areas. I would use a held shaped cardboard mask and mask on the 
fly rather than use plastic film and any overspill I would repaint. 
Finally color  ink washes from an airbrush would be used to enhance 
colors. Repaint where necessary. All good, lung-healthy fun!" 
  
 07a: Bloodrayn... I mean Durham Red! 
 70b: Muscular guy!
"7c: To aid me in this digital art replicating of an old style I was 
using Photoshop CS2. It's my preferred app and the brushes, with a 
little hard work and experimentation can be tweaked to give a pretty 
good look. I use some of the photoshops default chalk/dry media brushes 
as pencils and dip pens such as the "WALT" brush/pen I built through a 
series of trial and errors.  I used this brush  to sketch draw and ink 
this cover.  (So named after "Walt Simonson; I credit all my brushes to 
the artists that inspire them and this pen came about after months of 
looking at Walt's line art for a personal project.)
Other brushes have 
been sampled from real world paint daubs, scanned and given certain 
parameters. Some brushes will provide straight lines, but have no 
character. Other provide character but can't be used to create point to 
point straight lines.  Some create the more authentic spatter of a 
slightly sputtery airbrush that you can see also adds texture in the 
painted work. Some brushes work best in a precise way with a certain 
tool such as the smudge or dodge tools whilst others create a general 
textural noise that needs to be painted out."
 7c: Meet Walt!
" 08: Whilst  looking for rat ref, I found a perfect Dredd chin on this guy. He should be in comics!  ;)"
08: All hail King Carlos! 
"09: But  what to go with; expression-wise? Go with grim thin mouth of 
Dredd distain or the snarling sneer of a Dredd rebuke? It's these small 
details that an artist can agonize over, like colors that might seem 
irrelevant to the casual fan. But we CARE. ;)  (I took both to tonal 
completion before Tharg decided for me.)" 
 09: An open snarl or thin and grim? 
"10: I drew up the Dredd line art using the Walt brush that gives a sort
 of sketchy pencil. It's actually based on a biro brush I created so i 
could sign my contracts in the computer without having to print them out
 and scan them back in again. I'm such a cheapskate.
To get an ink pen look, I doubled up the art to make it darker, the ran a
 slight blur and levels on it to simulate the ink blobbing a bit. Once 
the overlay of colors goes on it, it darkens up quite nicely and I like 
the imperfections, as if the ink wasn't too pure or the scan not so 
perfect. Ironic I spend quite a lot of time trying to make it look "a 
bit crap" after seeking out the computer in the early days to make the 
job quicker and better! "
 10: Using Walt to get the biro look
"11: Here we see the art with a  gradient overlay in multiply layer  mode
 with the start of some highlighting to pick out a light source. I'm 
working with the art upside down to how it will be printed, Dredd 
hanging upside down so I have to remember light will be coming from 
below and just catching his chin. I have a few rat tails hanging up to 
suggest gravity but from what I've seen the little buggers seem to defy 
gravity." 
 11 - Working upsidedown...
"12: I've added some black here. I'm just toggling between black and 
white, and layer masks at that (I'll cover layer masks in a moment). I 
know I'm on the right tracks here when it's looking this grubby and 
murky.  This is how my real world painting used to look like at this 
stage, without the messy fingers!" 
 12 - Old Stony looking grubby and Murky!
"13: Painting some highlights back in and some mid tone. You can almost 
hear my sigh of relief I haven't cocked it all up. There is a plan of 
sorts although I do concede my art process can be considered "rescue 
art."  Twenty years I'm still learning but I love the process!" 
 13: Rescue art???
"14. What a difference a dropped on background makes. This would be the 
equivalent of painting around the figure to hide all the overspill and 
mistakes that artists would do. It's looking clearer and the tone has 
had a little texture applied courtesy of a my spatter airbrush." 
 14: A handy, dropped on background.
"15: The addition of colour!  (Seen here without the tonal layer, just the colour overlays.)" 
15: Beautiful! 
"16: For this and recent Dredd strip I used an approach I used for my 
textures, namely creating a separate file ("color package") made of 
individual colour layers in a group folder with layer masks I could drop 
onto tonal art work. I could then just quickly reveal the overlaying 
color by painting into its mask with white, correcting quickly if I 
strayed over the lines by painting black. Saves all that changing 
colours, plus the files allows for repeatable colours and predictable 
results. You can see the masks in action here.  I added a slight tonal 
offset; a watercolour wash texture to replicate inks drying in different 
concentrations in the wash. It sounds all very complicated, and it was. I
 dropped the process after a couple of strips as not really saving me 
much time."
16: Behold, Mark's textures!
"17: Like the colour package, I have a more successful package of texture 
layers in various layer modes as seen here. This replicates the texture 
"noise" artists sometimes give their work to make it less soft and flat.
 I based this particular collection on the work of Drew Struzan. Once 
again, it's all preset stuff that can be revealed or hidden with the 
layer masks to see what works. There's also  a levels and hues package 
that i no longer use that I had for improving contrast and tweaking the 
final look of the art."
17: The Drew Struzan collection! 
"18: This shows just the textures that went over the art. I use a 
gradient tool on the layer mask. You can see some almost sponge-stamped 
flecks of green have appeared on the yellow areas on the final art.  The
 background has a sewer grill shadow pattern to back and centre Dredd in
 a vague frame. Bit too colourful at this point."
18:  Mark sneezed into a hanky while working... 
"19: In fact aside from a black and white background  version (my 
favorite)  I did several versions of the background with different 
values and saturation. Over thinking it again?
Here is a rare glimpse into the secret world of Mark's Actions... (!)  I 
mean of course Photoshop actions, those wonderful time saving scripts of
 commands that can help on repetitive tasks. I use them so much I worry I
 might loose years of experimentation so I'm  constantly back them up. 
 Here you can see the "Walt refine fine line" that makes  sketchy art 
look like pen art. (I have one that turns line art drawn with the line 
tool look like it was drawn) The open action is to correct for 2000 AD's
 printers habit of darkening all my art, boosting the values in the 
shadows only."
 19: Action-packed image!
"20: The finished art I preferred:"
20: Black and White delight!  
"21: The Gallery of Inconsequential Agony: Cover variants I tried out for
 clarity and effect. Someone somewhere is screaming "WHY!"
21: The Gallery of Inconsequential Agony!
"22: The final piece. and what you finally got, which I think works just 
as well if a little more obvious. 90% of my preferred choices never make 
it to print because I'm too cutting edge and radical. (LOL!)
I wondered about the red lips sneer but I wanted more of a Clint 
reference to be there. It could be blood.  Also that light catching the 
chin. I like the pads. And the eagle tuned out better than expected.
Does it look like it was painted outside of the computer though?"     
22: Phew! The Final Image.
He says "Here are some bonus materials. "WaltBrush.abr" For any artists out there who want to have a go 
with the "Walt brush" (maybe I shouldn't name these brushes- guns yes- 
brushes no) here it is a freebie download. If you have a version of 
photoshop CS2 or later simply drop it in your brushes presets for your 
application and then load from the brushes drop down menu in Photoshop. 
Will work in PC and Mac versions of Photoshop. Some talent  maybe 
required."
Mark has also been kind enough to share his favourite hot tip, too - "Tired of your tablet pen skating around your tablet? Miss the 
drag of REAL paper but are too cheap to pay for overpriced nibs that 
simulate real pens? Then try the Harrison technique of taping a piece of
 paper to your tablet!  Pause mid stroke and not have the pen slip and 
stutter! It only took me 20 years to figure that out!  :)"
Wow, now there's a brilliant post! Thank you so, so much to Mr Harrison, I'm sure many will be inspired by the fantastic hints, tips and processes in this commentary! Look out for Mark's dazzling work in the prog soon...