An advantage of collage processes in general is they allow an infinite number of variations of an image to be tried out easily.  The method I've invented allows this benefit to be available until one is satisfied with the composition, as the gluing is done afterwards, and yet it ensures that the composition is not lost when it is taken apart to be glued.

The method is suitable for making paper collages each piece of which is overlapped in at least one place, either by another  piece or by the matt when the artwork is mounted.

The following instructions are for designing and making collages which are constructed with pieces of paper which are placed horizontally, across the composition, and which have an edge that is not at all overlapped.  The instructions in italics are for pieces which do not extend to the width of the composition.  I have provided these instructions where the method differs.  (If a piece borders the composition but does not extend right across it, I use a combination of both methods.)  The instructions can be adapted to make collages with other structures.

1. 

I colour the paper, usually with gouache and watercolour.  I sometimes overpaint this with acrylic ink. I usually colour three sheets of stretched watercolour paper.  When I remove the paper from the drawing board, I cut round the outside of the gummed strip.

2. 

 I tear or, occasionally, cut the paper to make collage pieces.  The pieces are usually strips of paper.  I sometimes use the back of the coloured paper if the colour has penetrated the torn edge at the back.

3. 

I add the new pieces to my collection. (I keep leftover pieces from my previous work.)
 

4. 

I compose the collage by juxtaposing and overlapping pieces, trying different pieces in various arrangements. I initially do this on a table but when I start to get an effect I like I tape the pieces to a wall or vertical board and work on it there.  The tape I use is drafting tape.  (Sometimes when I compose I make collage pieces as I go along, selecting from my coloured sheets areas I would like to try out.)

5.

When a composition I like starts to form, I tape strips of card over the areas that surround it to help me to see it.  I continue to compose, putting pieces in front of what is there already and the strips of card, until a composition I like has formed.

6. 

I put additional strips of card in front of the collage pieces surrounding the composition.  I then, if necessary, adjust the position of these strips to help me determine the exact location of the boundaries of the composition.  I measure the composition.

7. 

I determine which collage piece edges I want to colour.

8. 

I indicate where the boundaries of the composition are, near its corners with a pencil.  To enable me to do this, I lift the ends of the strips of card, untaping and retaping the strips as necessary.  I then remove the strips.

9. 

Using tape, I secure the construction at the front, outwith the composition.   Collage pieces which do not extend to the width of the composition are secured onto the construction with tape where the tape will not show, in two places.  I remove the construction from the board.  I then, on the reverse of the composition, secure with tape each collage piece in at least two places.  If a collage piece, at the back, is covered, I tear away a little of the paper that covers it so that some tape can be stuck down.

10. 

I cut unwanted paper from the borders of the construction, leaving a margin of an inch or so (if I have it) around the perimeter of the composition.  I first draw where the cuts will be, using a ruler and a pencil.  Before I cut I also ensure that the marks near the corners of the composition, which indicate where its boundaries are, extend a little into the margin.

11. 

 I stretch hot pressed watercolour paper and keep it stretched on the board.  It will be the support for the artwork.  (When hot pressed paper is not available I use "not" paper.)

12. 

Using the measurements of the composition, I draw pencil lines on the support paper to show where I want the boundaries of the composition to be.  I extend the lines to ensure that they are long enough to be seen when the construction is on the support.

13. 

I determine the order in which the collage pieces will be glued onto the support paper and number them accordingly.  I place the construction face down, and on the back of the collage piece which is uppermost I write the number one.  On the piece which is second uppermost I write the number two and so on. If there are pieces which are equal in this regard, I give them the same number but use letters to differentiate them, so I may have, for example, 2A and 2B.

14. 

I transcribe the numbers to the fronts of the pieces, avoiding the composition.

15. 

I place the artwork on the support paper in its planned position, and attach it in a few places with tape.

16. 

I draw a pencil line outside and around the perimeter of the composition, about 1/4" from its boundaries.

17.

I draw the shapes of tabs which will be used later as handles.  When collage pieces extend the width of the composition, I put the tabs at the ends of them, extending beyond the pencil lines.  I position them leading from areas of the artwork which are not overlapped and ensure when possible that they do not overlap each other.  Each piece should have at least two tabs, and at least two which are placed some distance apart.  I write the number of each piece on at least one of its tabs. 
     I do not put tabs on pieces which do not border the composition.

18. 

I put at least two registration marks at the ends of the tab shapes and on the support paper, and on the latter I number each group of marks with the number of the collage piece it is for.
     On the front of pieces which do not extend to the width of the composition and on the construction, I put two well-spaced pairs of registration marks.  I put them just under where the edge of an adjacent overlapping piece will lie.

19. 

On the front of collage pieces which are overlapped by other pieces, a pencil line is drawn along the area which is covered, 1/8" - 1/4 "away from where the edge of the overlapping piece lies.  I gently raise the overlapping edges of the overlapping papers with a finger, so I can insert the end of a pencil.  After drawing the lines I remove the construction from the support paper, and take it apart, discarding the tape.

20. 

To reduce unnecessary bulk, I tear away some of the surplus paper of each piece, working in numerical order and starting with piece (or pieces) number one.  When the gluing has been done, a collage piece can have ridges on it caused by the edge of a collage piece underneath; for this reason, when I tear off surplus paper, I compose the potential ridge to ensure that it doesn't jar with the composition.  The pencil lines help me do this and also show how far I can tear without risking making a hole in the artwork.  I ensure I don't remove any registration marks.  After each piece has been torn I tape it to its place on the support; as I do so I check whether the tearing of the previous piece has been done well.   I also ensure that there are no clusters of edges of paper that could cause bumps in paper to be placed above, and I ensure that, where possible, a good proportion of each piece will be adhered directly to the support paper.

When I remove surplus paper from pieces whose exposed edge or edges will be overlapped by another piece or pieces, I ensure there is enough paper left outside the area which will show, in at least two places which are some distance apart, for some tape to be applied.  These will serve as tabs.  (The unwanted edges which lead to the spots where two pieces will meet will be scraped later with a knife.)  The torn-away edge should blend with those of the piece or pieces adjacent to it.

    I put two well-spaced pairs of registration marks on the piece and on the support paper, and on the latter I number the marks  with the number of the collage piece they are for.  If necessary, I re-write the number on the piece.

21. 

Taking the construction apart again as required,  I cut along the line drawn outside the perimeter of the composition and on either side of the tab shapes.

22. 

I place any piece on the support in its planned position and secure it with tape where the tabs are (or where there is paper which will not show), avoiding what has been marked on them. I put several registration marks on the piece on the edge of the area to be overlapped and on the support paper, dispersing the marks well and placing one of them approximately half way along the piece.  (These marks should be erased later if the paper that is to cover them is not opaque.)  I remove the piece and on the support paper draw a loop around these registration marks, and write in it the  number of the piece.  I repeat this with the remainder of the collage pieces.  I ensure that the registration marks are not big enough to be visible in the composition.

23. 

I colour the edges of the pieces, where desired. I use dry media, usually pastel pencils.  I often re-assemble the composition to judge the effects of this and to help me decide how much to do.

24. 

I glue the pieces to the support in numerical order, starting with piece (or pieces) number one.  I first secure scrap paper onto my work surface with tape.  I (usually) draw an arrow on the back of the collage piece to indicate which edge (if any) is to show and then I place it on the scrap paper face down and secure it with tape where the tabs are.  Using my fingers I cover it with glue.  The film of glue must be thin, especially near the edge which will show, and I spread it just short of this edge.  (I find the edge areas easiest if I initially put the glue on thickly then place a piece of tissue paper over the area, run my fingertips over the tissue paper lightly and in an inward direction and then remove the tissue paper which has picked up the surplus glue.)  I do not glue the tabs.
The glue I use is (archival) Wet Mounting Adhesive or (archival, PVA) Neutral pH Adhesive.

25. 

I remove the tape from the tabs and, using the tabs as handles, I align the piece against its registration marks on the support.  The glue tends to make the paper expand a little, thus putting the registration marks out slightly. However, I find if I align the central registration mark accurately and the rest as closely as possible, my design is retained with a high degree of accuracy. I then let go of the piece and tape it down where the tabs are.

26. 

To protect it, I cover the piece with tissue paper, matt side downwards.  I secure the tissue paper with tape.  I then run my finger tips over the edge of the piece (with the tissue on top of it) in an inwards direction, so that if there is too much glue it is less likely to squirt out from beneath the piece I am sticking.  I then apply pressure on all the collage piece, through the tissue paper, pressing extra firmly at the edges.  If too much glue is now present, it will emerge and stick to the tissue paper.  If this occurs I repeat the pressing down with sheets of fresh tissue until it  no longer does so.

27. 

I weight each piece as it dries. I cover it with tissue paper, then a magazine and then heavy books.  I leave it for a few hours.

28. 

Overlapped Exposed Edges
As well as reducing paper with careful tearing, I reduce with a knife any edge which will be overlapped where it leads to the spot where two pieces will meet. I scrape this edge as it could cause an ugly ridge on the paper to be glued on top of it.  After the piece with this edge has been glued in place, and when the glue is dry, I make the edge smooth with a craft knife fitted with a blade with an outward curve.  To protect the design, I make and position a paper template of the overlapping edge of the overlapping piece beforehand.  If necessary I use a weight to keep the template in position while I'm using it. I ensure the scraped and cut area and the torn area merge well.

29. 

When the glue has dried, I remove the tape and, with a trimming knife, the tabs.  I leave the 1/4" border around the image.  I let the glue dry out thoroughly (I wait a few days) before I remove the artwork and support from the board, in order to reduce the risk of the support paper being warped.  I use a trimming knife to cut the artwork free. I leave a border of paper of indeterminate size around the artwork.

30. 

I erase the pencil lines drawn on the support paper and then, on the support paper near the corners of the artwork, I indicate afresh with short pencil lines where I'd like the boundaries of the composition to be.  This gives me an opportunity to revise their positions by a small degree, if I want to.