Here we will do a deepdive into all the different parts and the special colours and plastics used to make them in Norway.
Slotted bricks -
Automatic Binding Bricks (ABB)
When the slotted bricks first came to Norway they were of the Automatic Binding Bricks (ABB) type. Without any LEGO markings on the studs or underneath. This was most likely because LEGO in Denmark did not have an extra brick mould with LEGO markings available. They had just got them, and needed all themselves. The ABB mould only consisted of 2x2 and 2x4 bricks, with a slot on one short side or on both opposite short sides.
The colours for the ABB bricks in Norway were very unique. Basically all the colours used, except for the common white, was a special colour you could only find in Norway.
Blockletter
Then shortly after at the very end of 1953 or start of 1954 the "blockletter" mould arrived in Norway. It is known as the blockletter mould because of the blocky/bold LEGO name on the underside of the bricks. This mould consisted of 1x2, 2x3 and 2x4 bricks with the same slot positions as the ABB bricks. The 1x2 and 2x3 bricks being a new type of brick. The mould was in use at the same time as the ABB mould, so the two of them complemented eachother having brick types the other was missing.
Basically all the same colours were available for the blockletter bricks as the ABB bricks, with one addition, brown bricks. We have not found any brown ABB bricks so it is believed that this mould was out of use when the colour was introduced.
Blockletter with number
The blockletter with number mould is quite similar to the mould coming before and after. It has thinner letters on the underside, and a hatched in number towards one of the short sides. This number is like an id for the position the brick had in the mould. This mould was also sent from Denmark to Norway, around the middle of 1954. These bricks are a little uncommon in Norway due to the short production time. You can read why under the hatched inner surface bricks section below.
This was the first time a mould had all the brick sizes, 1x2, 2x2, 2x3 and 2x4. A new slot variation was also introduced for the 2x4 bricks in this mould. Having a slot on one short side as well as towards the opposite end of one long side. It was in use at an overlap at the end of the normal blockletter production. So a few of the special Norwegian colours (light red, light green, light yellow and brown) were still in use. It was also the first mould to use the Norwegian colour known as "ice-white", a kind of white with a blue hue.
Hatched inner surface
The hatched inner surface mould is the very first unique Norwegian mould. It was never used in Denmark. It is a retooled version of the blockletter with number mould. Meaning they used the same mould, but made some changes to it. It has the same thin LEGO logo underneath and the same brick types and slot positions. However they "refurbished" the underside of the brick removing the hatched in number and creating these thin lines on the surface. Hence the "hatched inner surface" name because of the surface having all the thin hatched lines/stripes.
The mould was introduced towards the end of 1954 and was in production until around 1956, making it one of the longest lasting moulds. This also shows as they are the easiest Norwegian bricks to find.
By late 1954 most of the unique Norwegian colours were out of production. Brown being the only colour that lasted a little longer. So hatched inner surface bricks are most commonly found in the basic LEGO colours, red, blue, white and yellow. Trans-clear was actually first used for this mould, never used for any of the earlier ones.
Maybe due to the long production run there were some differences in the basic colours. You can find hatched inner surface bricks in white as well as ice-white, red and a darker red, blue and dark blue (rare colour), yellow and a orangey-yellow.
Short beams
The short beams mould consisted of 2x8 and 2x10 bricks/beams with one slot. As well as 2x3 bricks with a special slot position similar to the one introduced for the blockletter with number 2x4. A slot on the short side as well as one towards the opposite end of one long side.
This mould was introduced shortly before the hatched inner surface mould. So a few beams managed to be made in the colours light red, light yellow and light green. These are very hard to find today, especially the light green.
Long beams
The long beams mould was introduced in 1955. It consisted of 2x12 and 2x14 bricks/beams. As well as other sizes, but we have not yet managed to confirm which. 2x2 and possibly 2x4 bricks seems likely as they show up in some Norwegian lots from time to time, but as mentioned we need to do more research.
No special colours for this mould as all unique Norwegian colours were discontinued by the end of 1954. So only red, blue, white and yellow.
The corner bricks may have been introduced around the same time as the long beams, most likely a little earlier. They use the same "dogbone" logo underneath the bricks. Possibly the corner bricks could have been a part of the same mould, but we need to do more research to find out what the mould sent to Norway actually consisted of. On the picture you can see the different types of dogbone bricks, it does not seem like all of them were available in Norway.
1x6 and 1x8 bricks
These bricks exist in two variations. With and without extra supports on the underside. The version without extra supports was released in early 1955, maybe late 1954. So far this variant has only been found in the ice-white colour in Norway, which makes the earlier date more likely. Late 1955 the new variation with extra supports were introduced replacing the old version. Only normal white and red has been found for the new version. Though blue, yellow and trans-clear has been found in other countries.
Single logo bricks
Released in 1955 this was the second unique Norwegian mould. Still no LEGO on the studs, but this mould introduced hollow studs. Meaning on the underside of the bricks you can see small holes inside each stud. The LEGO logo on the underside of this mould was slightly smaller and rounder.
This mould is identical to the later "double logo" bricks, minus the logo on the studs, hence the name "single logo".
The 2x4 bricks can be found with and without slots. Possibly making them the first "hollow bricks" (bricks without slots or tubes). This must have been a change done to the mould closer to 1956.
Hollow bricks
Hollow bricks is the common name for all LEGO bricks without tubes and slots. They were released the same time in Norway and Denmark, 1956. The basic hollow bricks mould had LEGO on the studs, the very first time LEGO bricks had this. They also had hollow studs and a small number underneath for the position of the brick in the mould.
In Norway they can be found in all the basic colours - red, white, blue, yellow and trans-clear.
Double logo "blockletter"
This mould combined the best of both worlds. Taking the bottom half of the previous "hollow stud blockletter" mould and the top of the new "hollow bricks" mould. This way a Frankenstein brick with LEGO on the studs, and on the underside, as well as having slots were created. In other words this became the third unique Norwegian mould, possibly also the most unique.
These bricks also exist without slots, being quite rare. The slots were probably closed/removed sometime during 1957. Marking the end of slotted bricks in Norway.
Tube bricks
Also just to mention it, from 1958 the new tube system was introduced in Norway as well, and they were the only types of bricks in production until the end.
Slotted bricks and windows could still be found in "pick a brick" boxes at toy stores, but this was just leftover stock.
Mystery bricks
Not long ago three mysterious bricks showed up in a lot in Norway. All three not matching any bricks we had seen before. When and why these were made we do not know, so we can only speculate. As there were a few bricks with factory mistakes in the lot, they may have originated from an employee. Maybe these bricks were made while a mould was being retooled? Could explain why they appear as a mix of different moulds, but no exact match.
The 2x4 does not say LEGO anywhere, but the colour and marble matches the 2x2. The 2x2 does say LEGO underneath, but it does not have hollow studs, same goes for the 2x3. The closest mould match would be the "hollow stud blockletter". Maybe this was the mould they were on they way to be retooled into.
On the top 2 pictures the bricks can be seen next to a common blue hollow brick. On the bottom two pictures the bricks can be seen with the closest matches from actual production moulds.