Washing an old Quilt
As for washing...in my first "real" quilt I used a vintage cotton batt that had been given to me my an elderly neighbor. This was in the 1960s and the batt was old THEN! This was not the nice glazed cotton batt we have today, nor even the ones I could have purchased in 1960. The batt was simply cotton layed out in a rather thick layer between sheets of paper which, of course, you removed when you sandwiched the loose cotton between top and bottom before quilting. The thickness reminds me of your quilt. The cotton was a "natural" color, meaning it was not WHITE. When the quilt was later very carefully washed, the dirty color of the cotton dirtied the yellow/white fabric of the quilt.
Therefore, I would suggest that you undo a seam somewhere and take a look at what is inside before you ever decide to wash.
I agree with Judy in Ohio, however. If the quilt is not "stinky" (some old quilts are!), you might consider not washing it.
If you must wash it, do so gently. The old bathtub method will work fine, although this is going to be a very heavy quilt when wet.
This is not a delicate quilt (no fancy stitching, no applique, no antique fabric falling to pieces, etc) so you could wash as I do, using the washing machine. Here's my method.
1. Fill the washing machine with cool water. Add some quilt detergent (or other suitable detergent) and make sure it is dissolved in the water. Turn machine OFF.
2. Add the quilt, press with your hands to agitate. Do not use the machine agitator. (I sometimes do use the machine to agitate for no more than a minute, standing there so I don't get involved in some other activity and forget!!) Swoosh the quilt up and down in the water with your hands. A short time is all that is necessary...you don't need to stand there for 20 minutes doing this. LOL.
3. Turn the machine to the spin cycle and spin out the wash water.
4. Refill with rinse water. Turn machine off. Again, hand agitate.
5. Turn the machine to spin and spin out the rinse water.
6. You may wish to repeat the rinse to insure all detergent is rinsed out.
7. Remove the quilt from the machine.
To dry the quilt I sometimes place it in the dryer for a minute or two...not long. Then I lay it over several clean towels laid on the floor. A fan helps create a drying breeze. Or you can do the same out in a shady spot on the lawn (over towels or clean sheets, etc). Or you can lay it over two or more clotheslines...this helps distribute the weight of the quilt. On small quilts I will hang from the clothesline by folding it and attaching the loose ends (not the folded edge) to the clothesline with multiple pins to distribute the weight. Three clothespins will not do it, believe me. LOL
On this quilt, be aware that washing/drying may cause the quilt to crinkle as quilts sometimes do...give it that more quilty look. This is a thick quilt...it may feel and look a bit thicker after washing.
The batting is thick.. this quilt will take a long time to dry. Remember that outdoors, in the shade, there may be birds nesting in the tree overhead. It is for this reason that I generally dry mine indoors. LOL.
If anyone else has ideas, please do add. Sorry this is long....