Well, first of all as an "S Corp" any charitable contributions are passed through separately on your K-1 and deducted personally as an itemized deduction.
Therefore the limitations are based upon your personal AGI.
The percentage limitation is based upon the type of charity that you are contributing to & what they are going to do with whatever you are going to give them (other than cash).
So you mention "artifacts", which will most likely require an independent appraisal to establish value.
It is likely that you are dealing with a 501c(3) organization so the question becomes are they going to sell the artifacts or are the artifacts going to a museum or similar organization that will use them in their collection which is open to the public.
Generally, the limitations that will apply would be 30% or 50% of your AGI.
Possibly, the issue of "stock in trade" (ie. inventory) would need to be evaluated if there has been any appreciation in the artifacts since you acquired them; the method that you acquired them could also be a factor if it was other than by a purchase with money or money's worth.
All that said, can you give me more specifics about the donation you are considering based upon the considerations identified above?