Naturally, this subject is very close to my heart. Well, it is what I make after all!
Before the renaissance period (1400-1700) most all paintings were done on solid mediums, such as wood. Did you know the Mona Lisa was on wood and not canvas? Nowadays almost all canvas's are stretched on stretcher bars of some description. However, do you know how vital the wood behind the canvas is to the overall perception and longevity of your canvas? A good retailer should be able at the very least to tell you the type of wood they are stretching their canvas over.
How do you join a stretcher bar?
There are a number of stretcher bar joins on the market today, some vastly better than others. Here's a list of the most common ones and what they mean for you. Take a look at a stretched canvas on your wall. Most likely one of the below will be used in the join.
The pros and cons of a traditional stretcher bar joint.
The pros to a traditional stretcher bar
The cons of a traditional stretcher bar
The pros and cons of a cut and pin strainer bar joint.
Pros of a cut and pin pre-assembled strainer frames
Cons of cut and pin pre-assembled strainer frames
The pros and cons of using a Wunderbars joint.
Pros of using Wunderbars Stretcher Bars
Cons of Wunderbars Stretcher Bars
Types of Wood Used in Stretcher bars
Stretcher bars come in various types of wood and there is not enough time to cover all of them in this post, but we'll go through the most common types and what you should be looking out for.
Pine - Whole and finger Joined - Most stretcher bars are made from pine. All of our traditional stretcher bars and two of the Wunderbars range are made from pine. We use Unsorted whole Scandinavian Pine, but finger joined is also common for standard stretcher bars. Bear in mind though that there are grades of wood..some with more knots and defects than others. The majority of pine used in stretcher bars will come from Scandinavia or one of the Eastern Bloc/Baltic countries such as Latvia or Estonia. The quality of a pine stretcher bar is good and is the most cost effective wood for producing a stretcher bar.
MDF - MDF is much more common amongst the larger stretched canvas providers, though it's brief popularity has faded lately. It's cheap and you wont find too many larger canvas's stretched on MDF. It's very much prone to bending. These will be amongst the cheapest stretched canvas's available on the market and will be cut and pinned as its almost impossible to make a traditional stretcher bar from them. Where possible ask what type of MDF is used, there's moisture resistant MDF which reacts and performs slightly better than standard MDF.
Fir and Paulowina Wood -Turn over your canvas. What does the wood look like? Cheaper stretcher bars will be thin (about 18mm in depth, though there are 38mm deep stretcher bars available in Fir) and probably look a little greenish/browny/pale in colour. This is most likely stretched on Fir or Paulownia wood. They are extremely fast growing trees and are in general imported from the Far East. They should have (if the retailer has bothered to include them) plastic corner keys in all four corners of the frame, sometimes one per corner, sometimes two. The wood should have a brittle appearance and be extremely light.
These stretcher bars are cheap. As cheap as they get and as you'd expect the quality of them can be very poor. Check to make sure the sides of the image on the canvas have no dips in them as these bars are prone to cracking and having large chunks missing. If it has it's likely this will show through in time on your image. Like with MDF this is OK for a run of the mill, throw it away item, but long term purchases, you should generally try to avoid them. Its most likely the seller is trying to save money buying cheap. There are far better options from the UK or Europe than these bars nowadays for a similar price.
Tulipwood or American Poplar - One of the the Rolls Royce's of stretcher bars. American poplar or Tulipwood as its more commonly known is a straight grained hardwood. It's used on a lot of higher quality stretched canvas. You know the Mona Lisa, that I was talking about before? Poplar wood…..Quality with these stretcher bars can last a lifetime. They come very smooth and green textured, but you may find some other colours like brown or even purple and black in the timber. Very, very, few knots and as such are ideal for larger canvas's where warping is more of an issue
Bendy, warpy, twisty! My stretcher bars on my canvas frame are warped!
Larger canvas's are prone to bowing or warping. You'll see a dip at the top of your canvas frame. This is due in some parts to the person who stretched the canvas (uneven tension) or the wood containing a lot of moisture then drying out, a massive knot in the wood or even the join of the stretcher bar. To alleviate this problem cross bars or braces should be used to stabilise the frame. Generally any frame over around 30" x 30" in size should have cross bars in them. If yours hasn't then you run the risk of it warping. Make sure you have cross bars where needed on your larger frames and that the supplier has used straight wood.
A good stretcher bar wood should be "kiln dried" which makes them sturdier and less likely to warp too. Wood is a porous material and as such it absorbs moisture. As the wood absorbs the moisture it expands and then shrinks when it starts to dry (like when you put the heating on). All this expanding and contracting, over time causes the wood to warp. Kiln dried wood reduces this problem somewhat.
Wood is known as a live product and in general all wood moves and warps constantly. This will happen to a greater or lesser degree depending on changes in humidity in the room you've hung it in and the species of wood used to stretch the canvas. Thinner wood also tends to warp more than thicker wood, so the bigger the frame the bigger the wood should be. Size matters again!
Is a knot a good knot or is it not?
Knots can cause your wood to warp. This warping will be more evident and pronounced in larger canvas's, so smaller canvas's shouldn't have too many issues, unless its a massive knot! Wood, as you know is a naturally occurring product. A Knot can be caused from either a part of a branch that's been enclosed by wood or a dead branch that's just dropped off the tree. Knots in stretcher bars can cause concern the bigger the stretcher bar you go. So the larger the frame the less knots you should have in them to keep the stability of the frame. Larger knots are the worse and if you have a good supplier then these should be cut out when manufacturing the stretcher bar. The manufacturer should also take time to assess how straight the bar is in their manufacturing process. Basically, when timber dries, knots don't dry at the same rate, so it can crack, fall out or cause the bars to twist. In general all softwoods are prone to the types of warp and twist, with knots, or without, even after the wood has been kiln dried. However, a good stretcher bar manufacturer should reduce the risk drastically in their quality control systems.
Keep in shape - Why a stretcher bar should have a slope or a lip
All, and yes, I mean ALL stretcher bars on canvas should have sloped or lipped edges. If the canvas is stretched over a flat/Square bit of wood then flat piece of wood is going to bleed or show on the image side of the canvas. If you have a precious canvas that's been stretched on square piece of wood, get it changed! Your canvas should only touch the beveled side and the back of the bar, not the image.
What to look for in a retailer in regard to stretcher bars?
The higher the quality stretcher bars the less problems you are going to have. When buying your stretched canvas you will need to decide how long you want the wood to last. Be prepared to pay more the deeper (protrudes from the wall) a bar you go and the higher quality of wood or the method you seek. Ask the seller what kind of bars they will be stretched on and what bar depths they go up to. Ask to look at their stretcher bars to examine the quality before you buy. If the retailer has an example on display, take it off the wall, turn it around, check the bars and how they look.
Stretcher bars may be unseen on the canvas but they are the engine room of what makes your picture stand out. If you want your canvas to last you need a good quality stretcher bar.
This is the final part to our guide
This is the final part to our buyers guide to framed canvas prints. Please let us know in the comments below if there's anything about your stretched canvas you want to ask or if there's anything we've missed. Also, if you get the opportunity, please share this post or link to it from your website, that'd be great!
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Tim Jones is one of the three owners of Wunderbars Limited. He's a little bit (very) obsessed with canvas stretching.