When you would like to display both sides of an artwork, you can construct a double-sided mat. (This can also work for related pieces that you would like to store back-to-back). For this style of double-sided mat, you close the front side, flip the entire mat over and open from that side to view the back. (The mat should be labeled to encourage this handling). A 3-D window cut out that is just slightly smaller than the back window mat may be helpful for supporting the artwork while it is in storage and being displayed, so that it does not sag in the window. Mylar support is often used if the work does not have friable or other incompatible media.
First, cut your window mats and make sure they fit well. Save a cut-out from the window to trim and use as a support if desired.
Next, you will hinge the back cover to the inner side of the second window mat. Attach a hinge to the back cover first (it should be narrow enough that the final outer hinge will be able to cover it).
Apply adhesive to only the half of the hinge that will join the back cover board. Fold your hinge to represent this point, apply PVA (or water) with a roller or brush to this segment, and then stretch taut and apply just barely covering your tick marks. Bone folder down and press under Hollytex, blotter and Plexi for a brief period. Once it is secure, attach this to the inside of the back window mat.
After the hinge is secure to the back mat, lay it hinge side down on the table. Keeping the window mat set open, lay this face down on top of the back mat, with the bare side aligned with the back mat hinge side. Make sure the edges are perfectly aligned, then weight this down.
Place some scrap paper under the exposed unadhered hinge cloth. Apply adhesive to the exposed part of the hinge, and remove your scrap paper.
Keeping everything well aligned, fold the hinge around the back of the window mat, pulling it taut around the spine edge but not stretching (a crepe eraser can help with gripping the cloth). Bone folder down, working from the middle to the edges so you don’t create bubbles or creases. Open and make sure the adhesive hasn’t seeped onto the face of the mat. Place Hollytex-lined blotter above and below the entire length of the hinge, add a Plexi strip along the entire hinge length, add weights, and leave to dry.
Your mat should now be in a z shape, like this:
Next add the front cover/ wrapper. Determine hinge width as for a standard window mat, and apply to the cover first, before joining it to the rest of the mat. (See step d under Basic Storage Mat for more specific instructions on this step).
Now place the cover hinge side down, with the hinge facing you. Take the window mats with back cover that you have constructed and place it face down on top. The inner window mat hinge will be on the side away from you, and the hinge connecting to the back mat will be nearest you. Apply adhesive to the protruding hinge cloth (except for the narrow area that will be around the spine edge). Pull the hinge taut around the spine edge (but don’t stretch it), pulling over the hinge already attached to the back mat (it should cover this neatly). Bone folder down, working from the middle to the edges so you don’t create bubbles or creases.
You can add an extra support for the piece to the back cover so it does not droop in the back window while sitting flat or in storage. Trim about 1/8” off 2 adjacent sides of the window cut-out that you kept, and adhere it to the back mat (with approved double-sided tape or other adhesive applied so that it will be secure but not warp the boards). You can mark the correct placement through the window mat, making sure the spine is in the closed position. If you use an awl or pin, the marks will not show later, as they would with pencil. Make sure it fits securely and evenly when the mat is closed.
Now you can install your piece by hinging or attaching a polyester sleeve the piece is secured into. Usually the piece is attached to the back part of the window mat, as there is less danger of disturbing it while opening from the front.