In my opinion, if you want to do something as delicate as that you won't be able to do it with hypertufa. Are you doing it with a mould, or straight from the leaf?

If doing it from a silicone mould...I'd mix up a slurry of cement/sand/SBR and paint it into the mould. Let that set for an hour or so, then make a mix of sand/cement/alkali-resistant glass fibre and pack it in to the depth you require.

After I posted I realized that I should have detailed the mix I was using. It is 1 part cement to 3 parts sand. I am doing it straight from the leaf on a flat surface. I havent found any fiberglass fibers yet and have just been using fiberglass drywall tape.

I might suggest you do this leaf on a mound of sand - and the use of drywall tape helps to reinforce the veins. There is a good thread in this forum - it deals w/ small leaves, but the ideas are helpful.

Best wishes

Vicki

Rainsend, my experience trying to do what you want involves lots of skinny leaves breaking off in your hands.... no matter how much fiber you use. Look at the picture below (and the 3 following it) to see what I finally did. It is not a leaf cast but it did turn out to be very pretty. The first photo shows the initial result and the next 3 show different views of the same paint job. I do not have a picture of the final product - the same paint job with a coating of exterior urethane that added darkness to the reddish color and a slight amber to the lighter areas.

I did this by coating the leaf with as "even" a coat of white cement (quickwall in this case) as I could get. ooops, I forgot an important step. FIRST, lay out a sheet of heavy clean plastic on a big sturdy table. Wad up a small amount of paper and decide how much to put under the center section of the leaf to give it alittle depth but still be able to put the leaf fronds flat on the table. It doesn't take much padding here - and JUST under the center vein area. NOW pick up the leaf and put it somewhere else and spray it with spray adhesive. I had some 10 year old can of stencil adhesive but I think anything would work. Next, go back to your clean plastic on the table and carefully (extra hands help here) lay the leaf down on the wads of paper and arrange each frond so it is separate from the others and push down so the adhesive makes the leaf parts stick to the plastic on the table. Get this all looking like you want and gently press down every edge so concrete won't seep under the leaf. NOW you can go back to spreading white cement very carefully on every part of your leaf. Try not to get much smeared off the leaf because you are going to have to clean up every bit before you go on.
When you are happy with your white cement coating (at least a quarter of an inch thick.... more on the big solid parts of the leaf), get all the edges like you want. Because you surely will have made a mess somewhere, now sprinkle clean sand over the plastic sheet and between every separate leaf part. DO NOT get much sand on top of the white cement).
Let all this dry for awhile. I waited about an hour.
Mix up a big pan of gray concrete and color it whatever color you want. I added a small amount of red powder (concrete colorant) someone gave me to try. I used a hypertufa recipe(on the dry side... not runny ) because this piece was going to get too heavy with just solid concrete.
The rest is easy and quick. You dump the colored (could be gray - just not white) mix over the leaf and pat it gently around so it covers everything and mounds up to the shape and thickness you want. Because the middle of this leaf is so deep, you need to have about a 2 to 4 inch thickness. Because you are using a mix that doesn't run, you can use your hands to give it a basic overall shape you like. All that sand you poured on the plastic will give the front of your piece a nice sandy finish which you will brush off later.

check out the photos and see if this would work for you
Laura

Here is a link that might be useful: try here

Vicki, My first attempt at this was putting the leaf on a mound. The cement/sand mixture ran right off the leaf sections. I suppose if I tried to do it solid maybe it would work.

Laura, That sounds like a good option for this type of leaf. I have put many hours into this project without success and am a bit frustrated at this point. The back pain alone caused problems with everything else I need to do. I like your leaf casting idea. Thanks.